feat(bokeh): implement line-stepwise (#2625)

## Implementation: `line-stepwise` - bokeh

Implements the **bokeh** version of `line-stepwise`.

**File:** `plots/line-stepwise/implementations/bokeh.py`

---
:robot: *[impl-generate
workflow](https://github.com/MarkusNeusinger/pyplots/actions/runs/20594558941)*

---------

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

Author: github-actions[bot]

plots/line-stepwise/implementations/bokeh.py

@@ -0,0 +1,82 @@
+""" pyplots.ai
+line-stepwise: Step Line Plot
+Library: bokeh 3.8.1 | Python 3.13.11
+Quality: 91/100 | Created: 2025-12-30
+"""
+
+import numpy as np
+from bokeh.io import export_png, output_file, save
+from bokeh.models import ColumnDataSource
+from bokeh.plotting import figure
+
+
+# Data - CPU usage readings over time with discrete state changes
+np.random.seed(42)
+n_points = 24
+hours = np.arange(n_points)
+
+# Create realistic CPU usage that stays at levels then jumps
+base_levels = [35, 45, 75, 85, 90, 80, 60, 40, 30, 25, 40, 55, 70, 85, 95, 90, 75, 60, 50, 45, 35, 30, 25, 20]
+cpu_usage = np.array(base_levels[:n_points], dtype=float)
+
+# Add small noise to make it realistic
+cpu_usage += np.random.uniform(-2, 2, n_points)
+cpu_usage = np.clip(cpu_usage, 0, 100)
+
+# Create step function data by duplicating points
+# For 'post' step style: value changes after the point
+x_step = []
+y_step = []
+for i in range(len(hours)):
+    x_step.append(hours[i])
+    y_step.append(cpu_usage[i])
+    if i < len(hours) - 1:
+        x_step.append(hours[i + 1])
+        y_step.append(cpu_usage[i])
+
+# Create data source
+source = ColumnDataSource(data={"x": x_step, "y": y_step})
+
+# Create figure
+p = figure(
+    width=4800,
+    height=2700,
+    title="line-stepwise · bokeh · pyplots.ai",
+    x_axis_label="Hour of Day",
+    y_axis_label="CPU Usage (%)",
+)
+
+# Plot step line
+p.line(x="x", y="y", source=source, line_width=4, line_color="#306998", line_alpha=0.9)
+
+# Add markers at actual data points for clarity
+marker_source = ColumnDataSource(data={"x": hours, "y": cpu_usage})
+
+p.scatter(x="x", y="y", source=marker_source, size=12, color="#306998", alpha=0.9)
+
+# Style text sizes 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
+p.xgrid.grid_line_alpha = 0.3
+p.ygrid.grid_line_alpha = 0.3
+p.xgrid.grid_line_dash = "dashed"
+p.ygrid.grid_line_dash = "dashed"
+
+# Background
+p.background_fill_color = "#fafafa"
+
+# Axis ranges
+p.y_range.start = 0
+p.y_range.end = 105
+
+# Save as PNG and HTML
+export_png(p, filename="plot.png")
+
+# Also save as HTML for interactive version
+output_file("plot.html")
+save(p)

plots/line-stepwise/metadata/bokeh.yaml

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+library: bokeh
+specification_id: line-stepwise
+created: '2025-12-30T10:38:37Z'
+updated: '2025-12-30T10:47:59Z'
+generated_by: claude-opus-4-5-20251101
+workflow_run: 20594558941
+issue: 0
+python_version: 3.13.11
+library_version: 3.8.1
+preview_url: https://storage.googleapis.com/pyplots-images/plots/line-stepwise/bokeh/plot.png
+preview_thumb: https://storage.googleapis.com/pyplots-images/plots/line-stepwise/bokeh/plot_thumb.png
+preview_html: https://storage.googleapis.com/pyplots-images/plots/line-stepwise/bokeh/plot.html
+quality_score: 91
+review:
+  strengths:
+  - Excellent step line implementation with manual coordinate transformation for post
+    step style
+  - Perfect title format following the spec-id · library · pyplots.ai convention
+  - Realistic CPU usage scenario that naturally demonstrates stepwise behavior
+  - Good visual clarity with appropriate font sizes for large canvas
+  - Proper use of ColumnDataSource for data management
+  - Clean, readable code following KISS principles
+  - Both PNG and HTML outputs provided for static and interactive viewing
+  weaknesses:
+  - Does not use Bokeh native step line mode (line with step_mode parameter) which
+    would be more idiomatic
+  - Missing HoverTool which would enhance the interactive HTML version
+  - Markers could be slightly larger for better visibility at the target resolution
+  - Small random noise in data slightly contradicts the discrete state changes concept
+    from the spec