feat(pygal): implement line-interactive (#2836)

## Implementation: `line-interactive` - pygal

Implements the **pygal** version of `line-interactive`.

**File:** `plots/line-interactive/implementations/pygal.py`

---
:robot: *[impl-generate
workflow](https://github.com/MarkusNeusinger/pyplots/actions/runs/20603328451)*

---------

Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>
Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>
Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

Author: github-actions[bot]

plots/line-interactive/implementations/pygal.py

@@ -0,0 +1,83 @@
+""" pyplots.ai
+line-interactive: Interactive Line Chart with Hover and Zoom
+Library: pygal 3.1.0 | Python 3.13.11
+Quality: 91/100 | Created: 2025-12-30
+"""
+
+import numpy as np
+import pandas as pd
+import pygal
+from pygal.style import Style
+
+
+# Data - Daily temperature readings for a weather station
+np.random.seed(42)
+dates = pd.date_range("2024-01-01", periods=365, freq="D")
+
+# Generate realistic temperature pattern with seasonal variation
+day_of_year = np.arange(365)
+base_temp = 15 + 12 * np.sin(2 * np.pi * (day_of_year - 80) / 365)  # Seasonal pattern
+noise = np.random.randn(365) * 3  # Daily variation
+temperature = base_temp + noise
+
+# Format dates for labels
+date_labels = [d.strftime("%b %d") for d in dates]
+
+# Custom style for pyplots
+custom_style = Style(
+    background="white",
+    plot_background="white",
+    foreground="#333333",
+    foreground_strong="#333333",
+    foreground_subtle="#666666",
+    colors=("#306998",),  # Python Blue
+    title_font_size=72,
+    label_font_size=48,
+    major_label_font_size=42,
+    legend_font_size=48,
+    value_font_size=36,
+    stroke_width=4,
+    opacity=".9",
+    opacity_hover=".95",
+    transition="400ms ease-in",
+    tooltip_font_size=36,
+    value_label_font_size=36,
+)
+
+# Create interactive line chart
+chart = pygal.Line(
+    width=4800,
+    height=2700,
+    style=custom_style,
+    title="Daily Temperature 2024 · line-interactive · pygal · pyplots.ai",
+    x_title="Date",
+    y_title="Temperature (°C)",
+    show_dots=True,
+    dots_size=6,
+    stroke_style={"width": 4, "linecap": "round", "linejoin": "round"},
+    show_x_guides=False,
+    show_y_guides=True,
+    x_label_rotation=45,
+    truncate_label=12,
+    show_legend=True,
+    legend_at_bottom=True,
+    legend_at_bottom_columns=1,
+    margin=60,
+    spacing=40,
+    x_labels_major_every=30,  # Show label every 30 days
+    show_minor_x_labels=False,
+    tooltip_border_radius=10,
+    js=[],  # Enable default JS for interactivity
+)
+
+# Add x-axis labels (show every 30 days for readability)
+chart.x_labels = date_labels
+
+# Add temperature data
+chart.add(
+    "Temperature", [{"value": float(t), "label": f"{date_labels[i]}: {t:.1f}°C"} for i, t in enumerate(temperature)]
+)
+
+# Save as PNG and HTML (interactive)
+chart.render_to_png("plot.png")
+chart.render_to_file("plot.html")

plots/line-interactive/metadata/pygal.yaml

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+library: pygal
+specification_id: line-interactive
+created: '2025-12-30T18:38:15Z'
+updated: '2025-12-30T18:40:27Z'
+generated_by: claude-opus-4-5-20251101
+workflow_run: 20603328451
+issue: 0
+python_version: 3.13.11
+library_version: 3.1.0
+preview_url: https://storage.googleapis.com/pyplots-images/plots/line-interactive/pygal/plot.png
+preview_thumb: https://storage.googleapis.com/pyplots-images/plots/line-interactive/pygal/plot_thumb.png
+preview_html: https://storage.googleapis.com/pyplots-images/plots/line-interactive/pygal/plot.html
+quality_score: 91
+review:
+  strengths:
+  - Clean seasonal temperature pattern with realistic daily variation demonstrates
+    time series well
+  - Excellent custom Style configuration with appropriate font sizes for large canvas
+  - Proper tooltip customization with formatted date and temperature values
+  - Good axis labeling with units (°C) and descriptive titles
+  - Smart x-axis label management showing only major labels every 30 days to prevent
+    clutter
+  - Outputs both PNG and HTML for static/interactive versions
+  weaknesses:
+  - PNG output is inherently static; the interactive features (hover, zoom, pan, range
+    selection) specified in the spec are only available in the HTML output - this
+    is a limitation of the PNG format, not a code issue
+  - Single data series limits feature demonstration; could show multiple locations
+    or metrics for comparison