Add delete event, perspective correction OCR, and OCR crop display

- Delete event: POST /event/{id}/delete removes DB row + files
- Perspective correction: minAreaRect on white plate region → getPerspectiveTransform
  gives a flat frontal view of the plate (e.g. 'GR B38 WR' instead of trapezoid)
- Tesseract now scales image 3x before OCR and skips EU blue strip (left 11%)
- Saves plate_ocr.jpg (perspective-corrected + enhanced crop actually fed to OCR)
- Event detail shows both raw detection crop and OCR crop side by side
- Manual plate edit form in event detail

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 delete_event(event_id: str):
+    conn = get_db()
+    conn.execute("DELETE FROM events WHERE id = ?", (event_id,))
+    conn.commit()
+    conn.close()
+
+
 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))