feat(pygal): implement line-annotated-events (#3139)

## Implementation: `line-annotated-events` - pygal

Implements the **pygal** version of `line-annotated-events`.

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

**Parent Issue:** #2997

---
:robot: *[impl-generate
workflow](https://github.com/MarkusNeusinger/pyplots/actions/runs/20627534098)*

---------

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-annotated-events/implementations/pygal.py

@@ -0,0 +1,92 @@
+""" pyplots.ai
+line-annotated-events: Annotated Line Plot with Event Markers
+Library: pygal 3.1.0 | Python 3.13.11
+Quality: 72/100 | Created: 2025-12-31
+"""
+
+import numpy as np
+import pygal
+from pygal.style import Style
+
+
+# Data - Stock price over a year with quarterly events
+np.random.seed(42)
+n_days = 250  # Trading days in a year
+
+# Generate realistic stock-like price data with trend
+base_price = 150
+returns = np.random.randn(n_days) * 0.012
+prices = base_price * np.cumprod(1 + returns)
+
+# Event data - indices and labels (quarterly earnings + product launch)
+events = [(31, "Q4 Earnings"), (94, "Q1 Earnings"), (136, "Product Launch"), (157, "Q2 Earnings"), (220, "Q3 Earnings")]
+
+# Custom style for 4800x2700 canvas with large fonts
+custom_style = Style(
+    background="white",
+    plot_background="#fafafa",
+    foreground="#333333",
+    foreground_strong="#1a1a1a",
+    foreground_subtle="#666666",
+    colors=("#306998", "#E74C3C", "#F39C12", "#9B59B6", "#27AE60", "#3498DB"),
+    title_font_size=72,
+    label_font_size=42,
+    major_label_font_size=38,
+    legend_font_size=42,
+    value_font_size=36,
+    value_label_font_size=34,
+    tooltip_font_size=32,
+    stroke_width=6,
+    font_family="sans-serif",
+)
+
+# Create XY chart for better control over coordinates
+chart = pygal.XY(
+    width=4800,
+    height=2700,
+    style=custom_style,
+    title="line-annotated-events · pygal · pyplots.ai",
+    x_title="Trading Day (2024)",
+    y_title="Stock Price (USD)",
+    show_dots=False,
+    stroke_style={"width": 6, "linecap": "round"},
+    show_legend=True,
+    legend_at_bottom=True,
+    legend_at_bottom_columns=3,
+    show_x_guides=False,
+    show_y_guides=True,
+    margin=100,
+    margin_bottom=200,
+    margin_left=200,
+    margin_right=100,
+    print_values=False,
+    interpolate="cubic",
+    range=(min(prices) * 0.95, max(prices) * 1.08),
+    xrange=(0, n_days),
+    x_labels_major_count=6,
+    show_minor_x_labels=False,
+)
+
+# Set numeric x-axis labels for trading days
+chart.x_labels = [0, 50, 100, 150, 200, 250]
+
+# Add main stock price line as XY coordinates
+price_data = [(i, prices[i]) for i in range(n_days)]
+chart.add("Stock Price", price_data, stroke_style={"width": 6})
+
+# Add event markers as separate dot series with vertical line effect
+# Each event gets its own series for clear legend labeling
+y_min = min(prices) * 0.95
+y_max = max(prices) * 1.08
+
+for event_idx, label in events:
+    # Create vertical line effect using multiple points
+    event_price = prices[event_idx]
+    # Vertical line from bottom to the event point
+    vertical_line = [(event_idx, y_min), (event_idx, event_price)]
+    # Add the vertical line with dashed effect
+    chart.add(label, vertical_line, stroke_style={"width": 4, "dasharray": "15, 10"}, show_dots=True, dots_size=18)
+
+# Render outputs
+chart.render_to_png("plot.png")
+chart.render_to_file("plot.html")

plots/line-annotated-events/metadata/pygal.yaml

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+library: pygal
+specification_id: line-annotated-events
+created: '2025-12-31T21:33:49Z'
+updated: '2025-12-31T22:33:44Z'
+generated_by: claude-opus-4-5-20251101
+workflow_run: 20627534098
+issue: 2997
+python_version: 3.13.11
+library_version: 3.1.0
+preview_url: https://storage.googleapis.com/pyplots-images/plots/line-annotated-events/pygal/plot.png
+preview_thumb: https://storage.googleapis.com/pyplots-images/plots/line-annotated-events/pygal/plot_thumb.png
+preview_html: https://storage.googleapis.com/pyplots-images/plots/line-annotated-events/pygal/plot.html
+quality_score: 72
+review:
+  strengths:
+  - Excellent use of pygal XY chart type for precise coordinate control
+  - Creative approach to simulate vertical event lines using line segments
+  - Good custom styling with appropriate font sizes for the large canvas
+  - Proper color differentiation for each event type
+  - Clean, well-structured code following KISS principles
+  - Realistic stock price data with proper volatility characteristics
+  weaknesses:
+  - Event labels appear only in the legend, not as text annotations directly on the
+    chart near the event markers (spec requests text labels at events)
+  - Vertical dashed lines could be more prominent (thicker stroke or bolder dashing)