feat(bokeh): implement contour-filled (#2516)

## Implementation: `contour-filled` - bokeh

Implements the **bokeh** version of `contour-filled`.

**File:** `plots/contour-filled/implementations/bokeh.py`

---
:robot: *[impl-generate
workflow](https://github.com/MarkusNeusinger/pyplots/actions/runs/20585401172)*

---------

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

Author: github-actions[bot]

plots/contour-filled/implementations/bokeh.py

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+""" pyplots.ai
+contour-filled: Filled Contour Plot
+Library: bokeh 3.8.1 | Python 3.13.11
+Quality: 90/100 | Created: 2025-12-30
+"""
+
+import numpy as np
+from bokeh.io import export_png, output_file, save
+from bokeh.models import BasicTicker, ColorBar, HoverTool, LinearColorMapper
+from bokeh.palettes import Viridis256
+from bokeh.plotting import figure
+from contourpy import contour_generator
+
+
+# Data - Terrain elevation surface with multiple peaks
+np.random.seed(42)
+x = np.linspace(-3, 3, 80)
+y = np.linspace(-3, 3, 80)
+X, Y = np.meshgrid(x, y)
+
+# Create surface with multiple Gaussian peaks (terrain elevation in meters)
+Z = (
+    1.5 * np.exp(-((X - 1) ** 2 + (Y - 1) ** 2))
+    + 2.0 * np.exp(-((X + 1.5) ** 2 + (Y + 0.5) ** 2) / 1.5)
+    + 1.0 * np.exp(-((X - 0.5) ** 2 + (Y + 1.5) ** 2) / 0.8)
+    - 0.5 * np.exp(-((X + 0.5) ** 2 + (Y - 1.5) ** 2) / 0.5)
+)
+
+# Scale to realistic elevation values (0-2000 meters)
+Z = (Z - Z.min()) / (Z.max() - Z.min()) * 2000
+
+# Create figure at 4800x2700 px with interactive tools
+p = figure(
+    width=4800,
+    height=2700,
+    title="contour-filled · bokeh · pyplots.ai",
+    x_range=(x.min(), x.max()),
+    y_range=(y.min(), y.max()),
+    tools="pan,wheel_zoom,box_zoom,reset,save",
+)
+
+# Explicitly set axis labels after figure creation
+p.xaxis.axis_label = "Distance East (km)"
+p.yaxis.axis_label = "Distance North (km)"
+
+# Color mapper for the filled surface
+color_mapper = LinearColorMapper(palette=Viridis256, low=Z.min(), high=Z.max())
+
+# Draw the filled surface using image
+p.image(image=[Z], x=x.min(), y=y.min(), dw=x.max() - x.min(), dh=y.max() - y.min(), color_mapper=color_mapper)
+
+# Overlay contour lines at specific levels for precise identification
+n_contour_lines = 12
+contour_levels = np.linspace(Z.min(), Z.max(), n_contour_lines + 2)[1:-1]
+
+# Create contour generator
+cont_gen = contour_generator(x=X, y=Y, z=Z)
+
+# Draw contour lines with high contrast (white with dark outline effect)
+for level in contour_levels:
+    lines = cont_gen.lines(level)
+    for line in lines:
+        # Draw white line for visibility on dark backgrounds
+        p.line(line[:, 0], line[:, 1], line_width=4, color="white", alpha=0.9)
+        # Draw thinner dark line on top for contrast on light backgrounds
+        p.line(line[:, 0], line[:, 1], line_width=1.5, color="#1a1a1a", alpha=0.8)
+
+# Add colorbar with terrain context
+color_bar = ColorBar(
+    color_mapper=color_mapper,
+    ticker=BasicTicker(desired_num_ticks=10),
+    label_standoff=25,
+    title="Terrain Elevation (m)",
+    title_text_font_size="22pt",
+    title_standoff=20,
+    major_label_text_font_size="18pt",
+    width=50,
+    padding=40,
+)
+p.add_layout(color_bar, "right")
+
+# Style text for large canvas
+p.title.text_font_size = "28pt"
+p.xaxis.axis_label_text_font_size = "22pt"
+p.yaxis.axis_label_text_font_size = "22pt"
+p.xaxis.major_label_text_font_size = "18pt"
+p.yaxis.major_label_text_font_size = "18pt"
+
+# Grid styling - subtle overlay grid (reduced alpha per review feedback)
+p.xgrid.grid_line_color = "white"
+p.ygrid.grid_line_color = "white"
+p.xgrid.grid_line_alpha = 0.3
+p.ygrid.grid_line_alpha = 0.3
+p.xgrid.grid_line_width = 2
+p.ygrid.grid_line_width = 2
+p.xgrid.grid_line_dash = [8, 4]
+p.ygrid.grid_line_dash = [8, 4]
+p.xgrid.level = "overlay"
+p.ygrid.level = "overlay"
+
+# Add hover tool for interactive elevation display
+# Create a grid of hover points for better interactivity
+hover_x, hover_y, hover_z = [], [], []
+step = 4  # Sample every 4th point for responsive hovering
+for i in range(0, len(x), step):
+    for j in range(0, len(y), step):
+        hover_x.append(x[i])
+        hover_y.append(y[j])
+        hover_z.append(round(Z[j, i], 1))
+
+# Add invisible scatter points for hover detection
+hover_renderer = p.scatter(hover_x, hover_y, size=30, fill_alpha=0, line_alpha=0, name="hover_points")
+hover_renderer.data_source.data["elevation"] = hover_z
+
+# Configure hover tool to show elevation values
+hover = HoverTool(
+    renderers=[hover_renderer],
+    tooltips=[("Location", "(@x{0.0} km E, @y{0.0} km N)"), ("Elevation", "@elevation{0} m")],
+    mode="mouse",
+)
+p.add_tools(hover)
+
+# Background
+p.background_fill_color = None
+p.border_fill_color = None
+
+# Save as PNG and HTML
+export_png(p, filename="plot.png")
+
+# Also save as HTML for interactive viewing with hover tooltips
+output_file("plot.html")
+save(p)

plots/contour-filled/metadata/bokeh.yaml

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+library: bokeh
+specification_id: contour-filled
+created: '2025-12-30T00:03:42Z'
+updated: '2025-12-30T00:36:43Z'
+generated_by: claude-opus-4-5-20251101
+workflow_run: 20585401172
+issue: 0
+python_version: 3.13.11
+library_version: 3.8.1
+preview_url: https://storage.googleapis.com/pyplots-images/plots/contour-filled/bokeh/plot.png
+preview_thumb: https://storage.googleapis.com/pyplots-images/plots/contour-filled/bokeh/plot_thumb.png
+preview_html: https://storage.googleapis.com/pyplots-images/plots/contour-filled/bokeh/plot.html
+quality_score: 90
+review:
+  strengths:
+  - Excellent use of Viridis colormap for colorblind accessibility and visual appeal
+  - Smart contour line styling with white base + dark outline for visibility across
+    all elevation levels
+  - Well-implemented terrain elevation scenario with realistic 0-2000m scale
+  - Clean integration of contourpy for precise contour line generation
+  - Proper text sizing for 4800x2700 canvas (28pt title, 22pt labels, 18pt ticks)
+  - HoverTool implementation provides interactivity in HTML output
+  weaknesses:
+  - Grid styling still somewhat prominent (alpha 0.3 with width 2); could be reduced
+    further for cleaner contour visualization
+  - Colorbar title is slightly small relative to other text elements