feat(matplotlib): implement crossword-basic (#7451)

## Implementation: `crossword-basic` - python/matplotlib

Implements the **python/matplotlib** version of `crossword-basic`.

**File:** `plots/crossword-basic/implementations/python/matplotlib.py`

**Parent Issue:** #3805

---
:robot: *[impl-generate
workflow](https://github.com/MarkusNeusinger/anyplot/actions/runs/26136422760)*

---------

Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>
Co-authored-by: Markus Neusinger <2921697+MarkusNeusinger@users.noreply.github.com>

Author: github-actions[bot]

plots/crossword-basic/implementations/python/matplotlib.py

@@ -1,25 +1,30 @@
-""" pyplots.ai
+""" anyplot.ai
 crossword-basic: Crossword Puzzle Grid
-Library: matplotlib 3.10.8 | Python 3.13.11
-Quality: 93/100 | Created: 2026-01-15
+Library: matplotlib 3.10.9 | Python 3.13.13
+Quality: 88/100 | Updated: 2026-05-20
 """
 
+import os
+
 import matplotlib.pyplot as plt
 import numpy as np
 from matplotlib.patches import Rectangle
 
 
+# Theme tokens
+THEME = os.getenv("ANYPLOT_THEME", "light")
+PAGE_BG = "#FAF8F1" if THEME == "light" else "#1A1A17"
+INK = "#1A1A17" if THEME == "light" else "#F0EFE8"
+INK_SOFT = "#4A4A44" if THEME == "light" else "#B8B7B0"
+CELL_WHITE = "#FFFFFF" if THEME == "light" else "#D0CEC8"
+CELL_BLACK = "#1A1A17" if THEME == "light" else "#050503"
+NUM_COLOR = "#009E73"  # Okabe-Ito position 1 (brand green) — sole colored element
+
 # Data: 15x15 crossword grid with 180-degree rotational symmetry
 # 0 = white (entry cell), 1 = black (blocked cell)
-np.random.seed(42)
-
 grid_size = 15
-
-# Create symmetric black cell pattern (traditional newspaper style)
-# Start with empty grid
 grid = np.zeros((grid_size, grid_size), dtype=int)
 
-# Define black cell positions for one half (will mirror for symmetry)
 black_cells = [
     (0, 4),
     (0, 10),
@@ -46,68 +51,63 @@
     (7, 12),
 ]
 
-# Set black cells and their symmetric counterparts
 for r, c in black_cells:
     grid[r, c] = 1
-    # 180-degree rotational symmetry
     grid[grid_size - 1 - r, grid_size - 1 - c] = 1
 
-# Calculate clue numbers (cells that start words across or down)
+# Calculate clue numbers (cells that start an across or down word)
 numbers = {}
 clue_num = 1
 
 for row in range(grid_size):
     for col in range(grid_size):
         if grid[row, col] == 1:
-            continue  # Skip black cells
-
+            continue
         starts_across = (col == 0 or grid[row, col - 1] == 1) and (col < grid_size - 1 and grid[row, col + 1] == 0)
         starts_down = (row == 0 or grid[row - 1, col] == 1) and (row < grid_size - 1 and grid[row + 1, col] == 0)
-
         if starts_across or starts_down:
             numbers[(row, col)] = clue_num
             clue_num += 1
 
-# Create plot (square format for crossword)
-fig, ax = plt.subplots(figsize=(12, 12))
+# Plot — square format (2400×2400 px) suits the 1:1 crossword grid
+fig, ax = plt.subplots(figsize=(6, 6), dpi=400, facecolor=PAGE_BG)
+ax.set_facecolor(PAGE_BG)
 
-# Draw the grid
 cell_size = 1.0
 
 for row in range(grid_size):
     for col in range(grid_size):
         x = col * cell_size
-        y = (grid_size - 1 - row) * cell_size  # Flip y-axis for proper orientation
+        y = (grid_size - 1 - row) * cell_size  # flip y so row 0 is at top
 
-        if grid[row, col] == 1:
-            # Black cell
-            rect = Rectangle((x, y), cell_size, cell_size, facecolor="#1a1a1a", edgecolor="#333333", linewidth=1.5)
-        else:
-            # White entry cell
-            rect = Rectangle((x, y), cell_size, cell_size, facecolor="white", edgecolor="#333333", linewidth=1.5)
+        face = CELL_BLACK if grid[row, col] == 1 else CELL_WHITE
+        rect = Rectangle((x, y), cell_size, cell_size, facecolor=face, edgecolor=INK_SOFT, linewidth=0.8)
         ax.add_patch(rect)
 
-        # Add clue number if this cell starts a word
         if (row, col) in numbers:
             ax.text(
-                x + 0.08,
-                y + cell_size - 0.08,
+                x + 0.07,
+                y + cell_size - 0.07,
                 str(numbers[(row, col)]),
-                fontsize=11,
+                fontsize=9,
                 fontweight="bold",
-                color="#306998",
+                color=NUM_COLOR,
                 ha="left",
                 va="top",
             )
 
-# Set axis properties
+# Outer border frame around the full grid
+border = Rectangle(
+    (0, 0), grid_size * cell_size, grid_size * cell_size, fill=False, edgecolor=INK, linewidth=2.5, zorder=10
+)
+ax.add_patch(border)
+
+# Style
 ax.set_xlim(0, grid_size * cell_size)
 ax.set_ylim(0, grid_size * cell_size)
 ax.set_aspect("equal")
 ax.axis("off")
-
-# Title
-ax.set_title("crossword-basic · matplotlib · pyplots.ai", fontsize=24, fontweight="bold", pad=20, color="#306998")
+ax.set_title("crossword-basic · python · matplotlib · anyplot.ai", fontsize=12, fontweight="medium", color=INK, pad=20)
 
 plt.tight_layout()
-plt.savefig("plot.png", dpi=300, bbox_inches="tight", facecolor="white")
+plt.savefig(f"plot-{THEME}.png", dpi=400, bbox_inches="tight", facecolor=PAGE_BG)