feat(highcharts): implement sn-curve-basic (#3865)

## Implementation: `sn-curve-basic` - highcharts

Implements the **highcharts** version of `sn-curve-basic`.

**File:** `plots/sn-curve-basic/implementations/highcharts.py`

**Parent Issue:** #3826

---
:robot: *[impl-generate
workflow](https://github.com/MarkusNeusinger/pyplots/actions/runs/21047248220)*

---------

Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>
Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

Author: github-actions[bot]

plots/sn-curve-basic/implementations/highcharts.py

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+""" pyplots.ai
+sn-curve-basic: S-N Curve (Wöhler Curve)
+Library: highcharts unknown | Python 3.13.11
+Quality: 91/100 | Created: 2026-01-15
+"""
+
+import tempfile
+import time
+import urllib.request
+from pathlib import Path
+
+import numpy as np
+from highcharts_core.chart import Chart
+from highcharts_core.options import HighchartsOptions
+from highcharts_core.options.series.area import LineSeries
+from highcharts_core.options.series.scatter import ScatterSeries
+from selenium import webdriver
+from selenium.webdriver.chrome.options import Options
+
+
+# Data: Simulated fatigue test results for steel specimens
+np.random.seed(42)
+
+# Generate realistic S-N curve data points with scatter
+stress_levels = np.array([450, 400, 350, 320, 300, 280, 260, 250, 240, 230, 220, 210])
+
+# Generate multiple test points per stress level with realistic scatter
+cycles_data = []
+stress_data = []
+
+for stress in stress_levels:
+    # Basquin equation: N = (S/A)^(-1/b)
+    A = 1200  # Material constant
+    b = 0.12  # Fatigue strength exponent
+    N_mean = (stress / A) ** (-1 / b)
+
+    # Add 2-4 test specimens per stress level with log-normal scatter
+    n_samples = np.random.randint(2, 5)
+    for _ in range(n_samples):
+        scatter = np.exp(np.random.normal(0, 0.3))
+        cycles_data.append(N_mean * scatter)
+        stress_data.append(stress + np.random.normal(0, 5))
+
+cycles = np.array(cycles_data)
+stress = np.array(stress_data)
+
+# Fit line using Basquin equation (log-linear fit)
+log_cycles = np.log10(cycles)
+log_stress = np.log10(stress)
+coeffs = np.polyfit(log_cycles, log_stress, 1)
+fit_cycles = np.logspace(2, 8, 100)
+fit_stress = 10 ** (coeffs[0] * np.log10(fit_cycles) + coeffs[1])
+
+# Material property reference values (typical for structural steel)
+ultimate_strength = 500  # MPa
+yield_strength = 350  # MPa
+endurance_limit = 200  # MPa
+
+# Create chart
+chart = Chart(container="container")
+chart.options = HighchartsOptions()
+
+# Chart configuration
+chart.options.chart = {
+    "type": "scatter",
+    "width": 4800,
+    "height": 2700,
+    "backgroundColor": "#ffffff",
+    "style": {"fontFamily": "Arial, sans-serif"},
+    "marginBottom": 150,
+    "marginLeft": 150,
+}
+
+# Title
+chart.options.title = {
+    "text": "sn-curve-basic · highcharts · pyplots.ai",
+    "style": {"fontSize": "48px", "fontWeight": "bold"},
+}
+
+# X-axis (logarithmic for cycles)
+chart.options.x_axis = {
+    "type": "logarithmic",
+    "title": {"text": "Number of Cycles to Failure (N)", "style": {"fontSize": "36px"}},
+    "labels": {"style": {"fontSize": "28px"}, "rotation": 0},
+    "min": 100,
+    "max": 100000000,
+    "gridLineWidth": 1,
+    "gridLineColor": "#cccccc",
+    "gridLineDashStyle": "Dash",
+    "tickInterval": 1,  # Show only major ticks (powers of 10)
+}
+
+# Y-axis (logarithmic for stress)
+chart.options.y_axis = {
+    "type": "logarithmic",
+    "title": {"text": "Stress Amplitude (MPa)", "style": {"fontSize": "36px"}},
+    "labels": {"style": {"fontSize": "28px"}},
+    "min": 150,
+    "max": 600,
+    "gridLineWidth": 1,
+    "gridLineColor": "#cccccc",
+    "gridLineDashStyle": "Dash",
+    "plotLines": [
+        {
+            "value": ultimate_strength,
+            "color": "#E53935",
+            "width": 4,
+            "dashStyle": "Dash",
+            "label": {
+                "text": f"Ultimate Strength ({ultimate_strength} MPa)",
+                "align": "right",
+                "style": {"fontSize": "24px", "color": "#E53935", "fontWeight": "bold"},
+                "x": -10,
+            },
+            "zIndex": 3,
+        },
+        {
+            "value": yield_strength,
+            "color": "#FB8C00",
+            "width": 4,
+            "dashStyle": "Dash",
+            "label": {
+                "text": f"Yield Strength ({yield_strength} MPa)",
+                "align": "right",
+                "style": {"fontSize": "24px", "color": "#FB8C00", "fontWeight": "bold"},
+                "x": -10,
+            },
+            "zIndex": 3,
+        },
+        {
+            "value": endurance_limit,
+            "color": "#43A047",
+            "width": 4,
+            "dashStyle": "Dash",
+            "label": {
+                "text": f"Endurance Limit ({endurance_limit} MPa)",
+                "align": "right",
+                "style": {"fontSize": "24px", "color": "#43A047", "fontWeight": "bold"},
+                "x": -10,
+            },
+            "zIndex": 3,
+        },
+    ],
+}
+
+# Legend
+chart.options.legend = {
+    "enabled": True,
+    "itemStyle": {"fontSize": "28px"},
+    "align": "right",
+    "verticalAlign": "top",
+    "layout": "vertical",
+    "x": -50,
+    "y": 80,
+}
+
+# Plot options
+chart.options.plot_options = {
+    "scatter": {
+        "marker": {"radius": 14, "symbol": "circle", "lineWidth": 2, "lineColor": "#ffffff"},
+        "states": {"hover": {"enabled": False}},
+    },
+    "line": {"lineWidth": 5, "marker": {"enabled": False}, "states": {"hover": {"enabled": False}}},
+}
+
+# Add test data scatter series
+scatter_series = ScatterSeries()
+scatter_series.data = [[float(c), float(s)] for c, s in zip(cycles, stress, strict=True)]
+scatter_series.name = "Test Data"
+scatter_series.color = "#306998"
+scatter_series.marker = {"fillColor": "#306998", "fillOpacity": 0.7}
+chart.add_series(scatter_series)
+
+# Add fitted S-N curve line series
+fit_series = LineSeries()
+fit_series.data = [[float(c), float(s)] for c, s in zip(fit_cycles, fit_stress, strict=True)]
+fit_series.name = "Basquin Fit"
+fit_series.color = "#FFD43B"
+chart.add_series(fit_series)
+
+# Add annotation series for fatigue regions (using invisible points with data labels)
+chart.options.annotations = [
+    {
+        "labels": [
+            {
+                "point": {"x": 500, "y": 420, "xAxis": 0, "yAxis": 0},
+                "text": "Low-Cycle<br>Fatigue",
+                "style": {"fontSize": "28px", "color": "#555555", "fontStyle": "italic"},
+                "backgroundColor": "transparent",
+                "borderWidth": 0,
+                "shadow": False,
+            },
+            {
+                "point": {"x": 100000, "y": 280, "xAxis": 0, "yAxis": 0},
+                "text": "High-Cycle<br>Fatigue",
+                "style": {"fontSize": "28px", "color": "#555555", "fontStyle": "italic"},
+                "backgroundColor": "transparent",
+                "borderWidth": 0,
+                "shadow": False,
+            },
+            {
+                "point": {"x": 50000000, "y": 180, "xAxis": 0, "yAxis": 0},
+                "text": "Infinite Life",
+                "style": {"fontSize": "28px", "color": "#555555", "fontStyle": "italic"},
+                "backgroundColor": "transparent",
+                "borderWidth": 0,
+                "shadow": False,
+            },
+        ],
+        "labelOptions": {"shape": "rect"},
+    }
+]
+
+# Credits
+chart.options.credits = {"enabled": False}
+
+# Download Highcharts JS and annotations module
+highcharts_url = "https://code.highcharts.com/highcharts.js"
+with urllib.request.urlopen(highcharts_url, timeout=30) as response:
+    highcharts_js = response.read().decode("utf-8")
+
+annotations_url = "https://code.highcharts.com/modules/annotations.js"
+with urllib.request.urlopen(annotations_url, timeout=30) as response:
+    annotations_js = response.read().decode("utf-8")
+
+# Generate HTML with inline scripts
+html_str = chart.to_js_literal()
+html_content = f"""<!DOCTYPE html>
+<html>
+<head>
+    <meta charset="utf-8">
+    <script>{highcharts_js}</script>
+    <script>{annotations_js}</script>
+</head>
+<body style="margin:0;">
+    <div id="container" style="width: 4800px; height: 2700px;"></div>
+    <script>{html_str}</script>
+</body>
+</html>"""
+
+# Write temp HTML and take screenshot
+with tempfile.NamedTemporaryFile(mode="w", suffix=".html", delete=False, encoding="utf-8") as f:
+    f.write(html_content)
+    temp_path = f.name
+
+chrome_options = Options()
+chrome_options.add_argument("--headless")
+chrome_options.add_argument("--no-sandbox")
+chrome_options.add_argument("--disable-dev-shm-usage")
+chrome_options.add_argument("--disable-gpu")
+chrome_options.add_argument("--window-size=4800,2800")  # Slightly taller to capture full chart
+
+driver = webdriver.Chrome(options=chrome_options)
+driver.get(f"file://{temp_path}")
+time.sleep(5)
+
+# Find the container element and take screenshot of just that element
+container = driver.find_element("id", "container")
+container.screenshot("plot.png")
+driver.quit()
+
+Path(temp_path).unlink()
+
+# Also save HTML for interactive version
+with open("plot.html", "w", encoding="utf-8") as f:
+    interactive_html = f"""<!DOCTYPE html>
+<html>
+<head>
+    <meta charset="utf-8">
+    <title>sn-curve-basic · highcharts · pyplots.ai</title>
+    <script src="https://code.highcharts.com/highcharts.js"></script>
+    <script src="https://code.highcharts.com/modules/annotations.js"></script>
+</head>
+<body style="margin:0;">
+    <div id="container" style="width: 100%; height: 100vh;"></div>
+    <script>{html_str}</script>
+</body>
+</html>"""
+    f.write(interactive_html)