feat(letsplot): implement parliament-basic (#2546)

## Implementation: `parliament-basic` - letsplot

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

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

---
:robot: *[impl-generate
workflow](https://github.com/MarkusNeusinger/pyplots/actions/runs/20585406402)*

---------

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/parliament-basic/implementations/letsplot.py

@@ -0,0 +1,104 @@
+# ruff: noqa: F405
+"""pyplots.ai
+parliament-basic: Parliament Seat Chart
+Library: lets-plot | Python 3.13
+Quality: pending | Created: 2025-12-30
+"""
+
+import os
+
+import numpy as np
+import pandas as pd
+from lets_plot import *  # noqa: F403
+
+
+LetsPlot.setup_html()
+
+# Data - Board of Directors composition (neutral, non-political)
+groups = [
+    "Finance Committee",
+    "Technology Board",
+    "Operations Division",
+    "Research Council",
+    "Marketing Team",
+    "Legal Advisory",
+]
+seats = [85, 72, 58, 35, 95, 55]
+# Colorblind-safe palette with distinct colors
+colors = ["#306998", "#FFD43B", "#E69F00", "#56B4E9", "#DC143C", "#9370DB"]
+
+total_seats = sum(seats)
+n_rows = 5
+
+# Calculate seat positions in semicircular arrangement (inline, KISS)
+row_weights = np.array([i + 1 for i in range(n_rows)])
+seats_per_row = (row_weights / row_weights.sum() * total_seats).astype(int)
+seats_per_row[-1] += total_seats - seats_per_row.sum()  # Adjust for rounding
+
+x_positions = []
+y_positions = []
+group_labels = []
+
+group_index = 0
+remaining_in_group = seats[0]
+
+for row_idx, row_seats in enumerate(seats_per_row):
+    radius = 0.5 + row_idx * 0.12  # Radius increases for outer rows
+    angles = np.linspace(np.pi, 0, row_seats)  # Semicircle from left to right
+
+    for angle in angles:
+        x = radius * np.cos(angle)
+        y = radius * np.sin(angle)
+        x_positions.append(x)
+        y_positions.append(y)
+        group_labels.append(groups[group_index])
+
+        remaining_in_group -= 1
+        if remaining_in_group == 0 and group_index < len(seats) - 1:
+            group_index += 1
+            remaining_in_group = seats[group_index]
+
+x_coords, y_coords, group_assignment = x_positions, y_positions, group_labels
+
+# Create DataFrame
+df = pd.DataFrame({"x": x_coords, "y": y_coords, "group": group_assignment})
+
+# Create legend labels with seat counts
+group_seat_counts = dict(zip(groups, seats, strict=True))
+df["group_label"] = df["group"].apply(lambda g: f"{g} ({group_seat_counts[g]})")
+
+# Create color mapping for labels
+label_colors = {f"{g} ({s})": c for g, s, c in zip(groups, seats, colors, strict=True)}
+color_values = [label_colors[label] for label in df["group_label"].unique()]
+
+# Build the plot
+plot = (
+    ggplot(df, aes(x="x", y="y", color="group_label"))
+    + geom_point(size=5, alpha=0.9)
+    + scale_color_manual(values=color_values)
+    + coord_fixed(ratio=1)
+    + theme_void()
+    + labs(title="parliament-basic · lets-plot · pyplots.ai", color="Division (Seats)")
+    + ggsize(1600, 900)
+    + theme(
+        plot_title=element_text(size=24, hjust=0.5),
+        legend_title=element_text(size=18),
+        legend_text=element_text(size=14),
+        legend_position="right",
+        plot_margin=[40, 40, 40, 40],
+    )
+)
+
+# Add majority line annotation (horizontal line at y=0)
+plot = plot + geom_hline(yintercept=0, color="#333333", size=1.5, alpha=0.6)
+
+# Add total seats annotation using geom_text with a data point
+annotation_df = pd.DataFrame(
+    {"x": [0], "y": [-0.15], "label": [f"Total: {total_seats} seats | Majority: {total_seats // 2 + 1}"]}
+)
+plot = plot + geom_text(data=annotation_df, mapping=aes(x="x", y="y", label="label"), size=14, color="#333333")
+
+# Save as PNG and HTML
+current_dir = os.getcwd()
+ggsave(plot, os.path.join(current_dir, "plot.png"), scale=3)
+ggsave(plot, os.path.join(current_dir, "plot.html"))

plots/parliament-basic/metadata/letsplot.yaml

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+library: letsplot
+specification_id: parliament-basic
+created: '2025-12-30T00:08:54Z'
+updated: '2025-12-30T00:27:32Z'
+generated_by: claude-opus-4-5-20251101
+workflow_run: 20585406402
+issue: 0
+python_version: 3.13.11
+library_version: 4.8.2
+preview_url: https://storage.googleapis.com/pyplots-images/plots/parliament-basic/letsplot/plot.png
+preview_thumb: https://storage.googleapis.com/pyplots-images/plots/parliament-basic/letsplot/plot_thumb.png
+preview_html: https://storage.googleapis.com/pyplots-images/plots/parliament-basic/letsplot/plot.html
+quality_score: 91
+review:
+  strengths:
+  - Excellent semicircular parliament visualization with clean concentric arcs
+  - Uses neutral non-political data context (board divisions instead of political
+    parties)
+  - Colorblind-safe palette with distinct, visually appealing colors
+  - Legend clearly shows division names with seat counts in parentheses
+  - Includes majority threshold annotation and total seats information
+  - Good use of theme_void for clean presentation
+  - Proper aspect ratio with coord_fixed
+  weaknesses:
+  - Title uses lets-plot with hyphen instead of letsplot (one word)
+  - Seats are distributed by row rather than strictly left-to-right across the semicircle