feat(letsplot): implement venn-basic (#2486)

## Implementation: `venn-basic` - letsplot

Implements the **letsplot** version of `venn-basic`.

**File:** `plots/venn-basic/implementations/letsplot.py`

---
:robot: *[impl-generate
workflow](https://github.com/MarkusNeusinger/pyplots/actions/runs/20584335161)*

---------

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

Author: github-actions[bot]

plots/venn-basic/implementations/letsplot.py

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+""" pyplots.ai
+venn-basic: Venn Diagram
+Library: letsplot 4.8.2 | Python 3.13.11
+Quality: 91/100 | Created: 2025-12-29
+"""
+
+import os
+
+import numpy as np
+import pandas as pd
+from lets_plot import *
+
+
+np.random.seed(42)
+
+LetsPlot.setup_html()
+
+# Data: Three research fields with overlapping expertise
+set_a_label = "Machine Learning"
+set_b_label = "Statistics"
+set_c_label = "Data Engineering"
+
+# Set sizes and intersections
+only_a = 45  # Only ML
+only_b = 35  # Only Statistics
+only_c = 30  # Only Data Engineering
+ab_only = 25  # ML & Statistics (not DE)
+ac_only = 15  # ML & DE (not Stats)
+bc_only = 20  # Stats & DE (not ML)
+abc = 10  # All three
+
+# Circle parameters (for 3-set Venn diagram) - larger for better canvas utilization
+r = 1.8  # radius (increased from 1.5)
+cx_a, cy_a = -0.85, 0.6  # Center of set A (top left)
+cx_b, cy_b = 0.85, 0.6  # Center of set B (top right)
+cx_c, cy_c = 0.0, -0.75  # Center of set C (bottom)
+
+# Generate circle points
+theta = np.linspace(0, 2 * np.pi, 100)
+
+# Create circle data
+circle_a_x = cx_a + r * np.cos(theta)
+circle_a_y = cy_a + r * np.sin(theta)
+circle_b_x = cx_b + r * np.cos(theta)
+circle_b_y = cy_b + r * np.sin(theta)
+circle_c_x = cx_c + r * np.cos(theta)
+circle_c_y = cy_c + r * np.sin(theta)
+
+# Create DataFrames for circles
+df_a = pd.DataFrame({"x": circle_a_x, "y": circle_a_y, "set": set_a_label})
+df_b = pd.DataFrame({"x": circle_b_x, "y": circle_b_y, "set": set_b_label})
+df_c = pd.DataFrame({"x": circle_c_x, "y": circle_c_y, "set": set_c_label})
+df_circles = pd.concat([df_a, df_b, df_c], ignore_index=True)
+
+# Label positions and values (adjusted for larger circles and better spacing)
+labels_data = pd.DataFrame(
+    {
+        "x": [
+            cx_a - 0.6,  # Only A (left side of A)
+            cx_b + 0.6,  # Only B (right side of B)
+            cx_c,  # Only C (bottom of C) - moved further down
+            (cx_a + cx_b) / 2,  # A & B intersection
+            (cx_a + cx_c) / 2 - 0.35,  # A & C intersection
+            (cx_b + cx_c) / 2 + 0.35,  # B & C intersection
+            0.0,  # Center (A & B & C)
+        ],
+        "y": [
+            cy_a + 0.4,  # Only A
+            cy_b + 0.4,  # Only B
+            cy_c - 0.75,  # Only C - moved much further down to avoid center overlap
+            cy_a + 0.75,  # A & B intersection
+            (cy_a + cy_c) / 2 - 0.4,  # A & C intersection
+            (cy_b + cy_c) / 2 - 0.4,  # B & C intersection
+            0.0,  # Center (A & B & C)
+        ],
+        "label": [str(only_a), str(only_b), str(only_c), str(ab_only), str(ac_only), str(bc_only), str(abc)],
+    }
+)
+
+# Set name labels (outside circles) - adjusted for larger circles
+set_labels_data = pd.DataFrame(
+    {
+        "x": [cx_a - 0.9, cx_b + 0.9, cx_c],
+        "y": [cy_a + 1.5, cy_b + 1.5, cy_c - 1.6],
+        "label": [set_a_label, set_b_label, set_c_label],
+    }
+)
+
+# Colors
+colors = {"Machine Learning": "#306998", "Statistics": "#FFD43B", "Data Engineering": "#DC2626"}
+
+# Create plot
+plot = (
+    ggplot()
+    + geom_polygon(aes(x="x", y="y", fill="set"), data=df_circles, alpha=0.35, color="white", size=2.5)
+    + geom_text(aes(x="x", y="y", label="label"), data=labels_data, size=20, fontface="bold", color="#1a1a1a")
+    + geom_text(aes(x="x", y="y", label="label"), data=set_labels_data, size=18, fontface="bold", color="#222222")
+    + scale_fill_manual(values=colors)
+    + coord_fixed(ratio=1)
+    + labs(title="venn-basic · lets-plot · pyplots.ai")
+    + theme_void()
+    + theme(
+        plot_title=element_text(size=28, face="bold", hjust=0.5), legend_position="none", plot_margin=[50, 30, 30, 30]
+    )
+    + ggsize(1200, 1200)
+)
+
+# Save as PNG and HTML
+ggsave(plot, "plot.png", scale=3)
+ggsave(plot, "plot.html")
+
+# Move files from lets-plot-images subdirectory to current directory
+if os.path.exists("lets-plot-images/plot.png"):
+    os.rename("lets-plot-images/plot.png", "plot.png")
+if os.path.exists("lets-plot-images/plot.html"):
+    os.rename("lets-plot-images/plot.html", "plot.html")
+if os.path.exists("lets-plot-images") and not os.listdir("lets-plot-images"):
+    os.rmdir("lets-plot-images")

plots/venn-basic/metadata/letsplot.yaml

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+library: letsplot
+specification_id: venn-basic
+created: '2025-12-29T22:53:27Z'
+updated: '2025-12-29T23:07:28Z'
+generated_by: claude-opus-4-5-20251101
+workflow_run: 20584335161
+issue: 0
+python_version: 3.13.11
+library_version: 4.8.2
+preview_url: https://storage.googleapis.com/pyplots-images/plots/venn-basic/letsplot/plot.png
+preview_thumb: https://storage.googleapis.com/pyplots-images/plots/venn-basic/letsplot/plot_thumb.png
+preview_html: https://storage.googleapis.com/pyplots-images/plots/venn-basic/letsplot/plot.html
+quality_score: 91
+review:
+  strengths:
+  - Excellent visual clarity with well-positioned labels and counts in all 7 regions
+  - Creative implementation using geom_polygon to construct Venn circles from coordinate
+    data
+  - Good color choices (blue/yellow/pink) with appropriate transparency for overlap
+    visualization
+  - Realistic and relatable data context (research field skills overlap)
+  - Proper title format and square aspect ratio appropriate for the diagram type
+  weaknesses:
+  - File output requires os workaround to move files from lets-plot-images subdirectory
+  - Could use geom_path instead of geom_polygon with size parameter for circle borders
+    (minor)