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/requirements.txt

@@ -6,3 +6,4 @@ requests==2.32.3
 opencv-python-headless==4.10.0.84
 numpy==1.26.4
 onnxruntime==1.20.0
+pytesseract==0.3.13