feat(pygal): implement errorbar-asymmetric (#2811)

## Implementation: `errorbar-asymmetric` - pygal

Implements the **pygal** version of `errorbar-asymmetric`.

**File:** `plots/errorbar-asymmetric/implementations/pygal.py`

---
:robot: *[impl-generate
workflow](https://github.com/MarkusNeusinger/pyplots/actions/runs/20602451830)*

---------

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/errorbar-asymmetric/implementations/pygal.py

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+""" pyplots.ai
+errorbar-asymmetric: Asymmetric Error Bars Plot
+Library: pygal 3.1.0 | Python 3.13.11
+Quality: 88/100 | Created: 2025-12-30
+"""
+
+import pygal
+from pygal.style import Style
+
+
+# Data - Material strength testing (MPa) with asymmetric confidence intervals
+materials = ["Steel", "Aluminum", "Titanium", "Copper", "Brass", "Bronze"]
+# Central values (median strength)
+y_values = [250, 150, 450, 200, 180, 220]
+# Asymmetric errors - showing realistic variation in error distribution
+# Some materials have larger lower errors (conservative bounds), others have larger upper errors
+error_lower = [35, 12, 20, 25, 8, 18]  # 10th percentile distance from median
+error_upper = [20, 28, 50, 15, 22, 30]  # 90th percentile distance from median
+# Now Steel and Copper have larger lower than upper (conservative), others have larger upper
+
+# Cap width for horizontal lines at error bar ends (in x-axis units)
+# Wider caps for clear visibility as proper horizontal lines (approx 1/3 of spacing between bars)
+cap_width = 0.35
+
+# Custom style for 4800x2700 canvas with larger fonts
+custom_style = Style(
+    background="white",
+    plot_background="white",
+    foreground="#333333",
+    foreground_strong="#333333",
+    foreground_subtle="#666666",
+    colors=("#306998", "#306998", "#306998", "#306998", "#306998", "#306998", "#306998"),
+    title_font_size=84,
+    label_font_size=52,
+    major_label_font_size=48,
+    legend_font_size=52,
+    value_font_size=42,
+    stroke_width=7,
+    opacity=1.0,
+    transition="0s",
+)
+
+# Create XY chart for error bar visualization
+chart = pygal.XY(
+    width=4800,
+    height=2700,
+    style=custom_style,
+    title="errorbar-asymmetric · pygal · pyplots.ai",
+    x_title="Material",
+    y_title="Tensile Strength (MPa)",
+    show_legend=True,
+    legend_at_bottom=False,
+    legend_box_size=28,
+    show_y_guides=True,
+    show_x_guides=False,
+    print_values=False,
+    margin=120,
+    stroke=True,
+    dots_size=8,
+    range=(80, 550),
+    xrange=(0, 7),
+    x_labels=["", "Steel", "Aluminum", "Titanium", "Copper", "Brass", "Bronze"],
+    x_labels_major_every=1,
+    show_minor_x_labels=False,
+)
+
+# Add each error bar with proper caps (horizontal lines at ends)
+for i in range(len(materials)):
+    x_pos = i + 1
+    y_center = y_values[i]
+    y_low = y_center - error_lower[i]
+    y_high = y_center + error_upper[i]
+
+    # Vertical error bar segment
+    bar_data = [(x_pos, y_low), (x_pos, y_high)]
+
+    # Bottom cap (horizontal line)
+    bottom_cap = [(x_pos - cap_width, y_low), (x_pos + cap_width, y_low)]
+
+    # Top cap (horizontal line)
+    top_cap = [(x_pos - cap_width, y_high), (x_pos + cap_width, y_high)]
+
+    # Only first bar gets legend entry
+    if i == 0:
+        chart.add("10th-90th Percentile Range", bar_data, stroke=True, show_dots=False, stroke_style={"width": 7})
+    else:
+        chart.add(None, bar_data, stroke=True, show_dots=False, stroke_style={"width": 7})
+
+    # Add caps as visible horizontal lines (thicker stroke for clarity as proper T-caps)
+    chart.add(None, bottom_cap, stroke=True, show_dots=False, stroke_style={"width": 12})
+    chart.add(None, top_cap, stroke=True, show_dots=False, stroke_style={"width": 12})
+
+# Add central points as main series (on top of error bars)
+central_data = [(i + 1, y_values[i]) for i in range(len(materials))]
+chart.add("Median Strength", central_data, stroke=False, dots_size=24)
+
+# Render to files
+chart.render_to_file("plot.html")
+chart.render_to_png("plot.png")

plots/errorbar-asymmetric/metadata/pygal.yaml

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+library: pygal
+specification_id: errorbar-asymmetric
+created: '2025-12-30T17:48:43Z'
+updated: '2025-12-30T18:17:17Z'
+generated_by: claude-opus-4-5-20251101
+workflow_run: 20602451830
+issue: 0
+python_version: 3.13.11
+library_version: 3.1.0
+preview_url: https://storage.googleapis.com/pyplots-images/plots/errorbar-asymmetric/pygal/plot.png
+preview_thumb: https://storage.googleapis.com/pyplots-images/plots/errorbar-asymmetric/pygal/plot_thumb.png
+preview_html: https://storage.googleapis.com/pyplots-images/plots/errorbar-asymmetric/pygal/plot.html
+quality_score: 88
+review:
+  strengths:
+  - Clear visualization of asymmetric error bars using pygal XY chart creatively
+  - Well-labeled axes with units (MPa for strength, Material for x-axis)
+  - Realistic engineering context (material tensile strength testing)
+  - Good demonstration of asymmetric errors with varied patterns across materials
+  - Clean code structure following KISS principles
+  - Proper title format and legend explaining what the percentile ranges represent
+  weaknesses:
+  - Legend symbols do not perfectly match the plot elements (squares in legend vs
+    lines/dots in plot)
+  - Layout has some unused whitespace on the sides
+  - Error bar caps could be more visually prominent