feat: PM2D standalone shape-based matcher

Programma standalone Pattern Matching 2D con GUI cv2/tk + algoritmo
puro riusabile. Due backend:

- LineShapeMatcher (default): porting Python di line2Dup (linemod-style)
  - Gradient orientation quantized 8-bin modulo π + spreading
  - Feature sparse top-magnitude con spacing minimo
  - Score via shift-add vettorizzato numpy (O(N_features·H·W))
  - Piramide multi-risoluzione con pruning varianti al top-level
  - Supporto mask binaria per modello non-rettangolare

- EdgeShapeMatcher (fallback): Canny + matchTemplate multi-rotazione

GUI separata da algoritmo. Benchmark clip.png (13 istanze):
  - Edge backend:  84s, 6/13 score ~0.3
  - Line backend:  4.1s, 13/13 score 0.98-1.00

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

main.py

@@ -0,0 +1,26 @@
+"""Entry-point standalone Pattern Matching 2D shape-based.
+
+Esegui:  uv run python main.py
+"""
+from pathlib import Path
+
+from pm2d.gui import run
+
+
+if __name__ == "__main__":
+    test_dir = Path(__file__).parent / "Test"
+    run(
+        initial_dir=str(test_dir) if test_dir.is_dir() else None,
+        angle_range_deg=(0.0, 360.0),
+        angle_step_deg=5.0,
+        scale_range=(1.0, 1.0),
+        scale_step=0.1,
+        num_features=96,
+        weak_grad=30.0,
+        strong_grad=60.0,
+        spread_radius=5,
+        pyramid_levels=3,
+        min_score=0.55,
+        max_matches=25,
+        backend="line",
+    )