Improve LPR accuracy and add manual plate edit

- Tiled YOLO (3x2, 20% overlap): plate confidence 0.307 -> 0.838 on test frame
- Aspect ratio filter (2.0-6.5:1): rejects non-plate shapes
- Confidence threshold 0.03 -> 0.04: removes fence/noise false positives
- Exclude top 15% (sky) and bottom 8% (timestamp overlay) from detection zone
- Add Tesseract as primary OCR (better for Latin plates), PaddleOCR as fallback
- Enhance plate crop before OCR: CLAHE + sharpening + min 80px upscale
- Save plate_crop.jpg (4x upscaled) to event dir for manual review
- Show plate crop in event detail page
- Add manual plate edit form in event detail (POST /event/{id}/plate)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/database.py

@@ -107,6 +107,13 @@ def get_event(event_id: str) -> dict | None:
     return dict(row) if row else None
 
 
+def update_plate(event_id: str, plate: str):
+    conn = get_db()
+    conn.execute("UPDATE events SET plate = ? WHERE id = ?", (plate.strip().upper() or None, event_id))
+    conn.commit()
+    conn.close()
+
+
 def get_cameras():
     conn = get_db()
     rows = conn.execute("SELECT DISTINCT camera FROM events ORDER BY camera").fetchall()