feat(highcharts): implement ridgeline-basic (#549)

## Summary
Implements `ridgeline-basic` for **highcharts**.

**Parent Issue:** #539
**Base Branch:** `plot/ridgeline-basic`

## Files
- `plots/ridgeline-basic/implementations/highcharts.py`

## Preview
Preview will be uploaded to GCS staging after this workflow completes.

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

Author: claude[bot]

plots/ridgeline-basic/implementations/highcharts.py

@@ -0,0 +1,232 @@
+"""
+ridgeline-basic: Ridgeline Plot
+Library: highcharts
+"""
+
+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 AreaSplineSeries
+from selenium import webdriver
+from selenium.webdriver.chrome.options import Options
+
+
+# Simple KDE implementation using Gaussian kernel
+def gaussian_kde(data, x_points, bandwidth=None):
+    """Compute kernel density estimate using Gaussian kernel."""
+    n = len(data)
+    if bandwidth is None:
+        bandwidth = 1.06 * np.std(data) * n ** (-1 / 5)
+    density = np.zeros_like(x_points, dtype=float)
+    for xi in data:
+        density += np.exp(-0.5 * ((x_points - xi) / bandwidth) ** 2)
+    density /= n * bandwidth * np.sqrt(2 * np.pi)
+    return density
+
+
+# Data - Monthly temperature distributions
+np.random.seed(42)
+months = ["Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"]
+base_temps = [5, 7, 12, 16, 20, 24, 26, 25, 21, 15, 10, 6]
+
+# Generate distributions for each month
+n_samples = 200
+distributions = {}
+for i, month in enumerate(months):
+    distributions[month] = np.random.normal(base_temps[i], 3, n_samples)
+
+# KDE parameters - temperature range
+x_range = np.linspace(-5, 35, 150)
+
+# Color palette (gradient from cool to warm colors)
+colors = [
+    "#306998",  # Python Blue (Jan - winter)
+    "#3B7CA5",  # Feb
+    "#4B8FB0",  # Mar
+    "#5CA2B5",  # Apr
+    "#6DB5B8",  # May
+    "#7EC8B0",  # Jun
+    "#059669",  # Jul - Teal Green (summer)
+    "#5CA87A",  # Aug
+    "#8FB85A",  # Sep
+    "#C2C83A",  # Oct
+    "#FFD43B",  # Nov - Python Yellow
+    "#306998",  # Dec - back to winter
+]
+
+# Create chart with container
+chart = Chart(container="container")
+chart.options = HighchartsOptions()
+
+# Chart configuration - standard (not inverted) for horizontal ridgelines
+chart.options.chart = {
+    "type": "areaspline",
+    "width": 4800,
+    "height": 2700,
+    "backgroundColor": "#ffffff",
+    "spacing": [80, 80, 80, 150],
+}
+
+# Title
+chart.options.title = {
+    "text": "Monthly Temperature Distribution",
+    "style": {"fontSize": "56px", "fontWeight": "bold"},
+    "y": 40,
+}
+
+# Subtitle
+chart.options.subtitle = {
+    "text": "Daily temperature variation by month (Ridgeline Plot)",
+    "style": {"fontSize": "36px", "color": "#666666"},
+    "y": 90,
+}
+
+# X-axis - Temperature values
+chart.options.x_axis = {
+    "title": {"text": "Temperature (°C)", "style": {"fontSize": "40px"}},
+    "labels": {"style": {"fontSize": "32px"}},
+    "min": -5,
+    "max": 35,
+    "tickInterval": 5,
+    "gridLineWidth": 1,
+    "gridLineColor": "rgba(0, 0, 0, 0.08)",
+}
+
+# Build y-axis labels for months
+y_axis_labels = []
+for i, month in enumerate(months):
+    y_pos = (len(months) - 1 - i) * 0.7 + 0.3  # overlap_factor
+    y_axis_labels.append(
+        {
+            "value": y_pos,
+            "width": 0,
+            "label": {
+                "text": month,
+                "align": "right",
+                "x": -20,
+                "style": {"fontSize": "32px", "fontWeight": "bold", "color": colors[i]},
+            },
+        }
+    )
+
+# Y-axis - Hidden, distributions use relative positioning
+chart.options.y_axis = {
+    "title": {"text": None},
+    "labels": {"enabled": False},
+    "gridLineWidth": 0,
+    "min": 0,
+    "max": 12,  # 12 months
+    "plotLines": y_axis_labels,
+}
+
+# Plot options for ridgeline appearance
+chart.options.plot_options = {
+    "areaspline": {"fillOpacity": 0.7, "lineWidth": 2, "marker": {"enabled": False}, "trackByArea": True},
+    "series": {"states": {"hover": {"enabled": True, "lineWidthPlus": 1}}, "animation": False},
+}
+
+# Create series for each month (Jan at top, Dec at bottom)
+overlap_factor = 0.7  # Controls vertical overlap between distributions
+scale_factor = 0.9  # Controls height of each distribution
+
+for i, month in enumerate(months):
+    # Calculate KDE for this month's distribution
+    density = gaussian_kde(distributions[month], x_range)
+    # Normalize density to [0, 1]
+    density = density / density.max()
+
+    # Calculate y-offset for this month (Jan at top = index 11, Dec at bottom = index 0)
+    y_offset = (len(months) - 1 - i) * overlap_factor
+
+    # Create data points: [x, y] where y = offset + scaled_density
+    data_points = []
+    for x_val, d_val in zip(x_range, density, strict=True):
+        data_points.append([float(x_val), float(y_offset + d_val * scale_factor)])
+
+    series = AreaSplineSeries()
+    series.name = month
+    series.data = data_points
+    series.color = colors[i]
+    series.fill_opacity = 0.75
+    series.line_color = colors[i]
+    series.line_width = 2
+    series.threshold = float(y_offset)  # Fill from this baseline
+
+    chart.add_series(series)
+
+# Legend
+chart.options.legend = {"enabled": False}
+
+# Credits
+chart.options.credits = {"enabled": False}
+
+# Tooltip
+chart.options.tooltip = {
+    "enabled": True,
+    "headerFormat": "<b>{series.name}</b><br/>",
+    "pointFormat": "Temperature: {point.x:.1f}°C",
+    "style": {"fontSize": "28px"},
+}
+
+# Download Highcharts JS
+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")
+
+# 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>
+</head>
+<body style="margin:0;">
+    <div id="container" style="width: 4800px; height: 2700px;"></div>
+    <script>{html_str}</script>
+</body>
+</html>"""
+
+# Save HTML file for interactive version
+with open("plot.html", "w", encoding="utf-8") as f:
+    html_output = (
+        """<!DOCTYPE html>
+<html>
+<head>
+    <meta charset="utf-8">
+    <script src="https://code.highcharts.com/highcharts.js"></script>
+</head>
+<body style="margin:0;">
+    <div id="container" style="width: 100%; height: 100vh;"></div>
+    <script>"""
+        + html_str
+        + """</script>
+</body>
+</html>"""
+    )
+    f.write(html_output)
+
+# 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=4800,2700")
+
+driver = webdriver.Chrome(options=chrome_options)
+driver.get(f"file://{temp_path}")
+time.sleep(5)
+driver.save_screenshot("plot.png")
+driver.quit()
+
+Path(temp_path).unlink()