feat: add OCR text extraction and Postgres full-text search

- Create ocr_text table for storing per-region OCR results
- Add tsvector search_vector column to photos with GIN index and
  auto-update trigger on filename/user_title/user_notes
- Implement ocr_photo Celery task using rapidocr-onnxruntime
- Add FTS leg to hybrid search: queries photos.search_vector and
  ocr_text via UNION, fused with semantic results via RRF (k=60)

Migration 0004 backfills search_vector for existing rows.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/app/tasks/vision.py

@@ -92,8 +92,44 @@ def vision_fanout(photo_id: str):
 
 @shared_task(name='ocr_photo', queue='vision')
 def ocr_photo(photo_id: str):
-    """OCR a photo — implemented in PR5."""
-    return {'status': 'not_implemented'}
+    """Run OCR on a photo and store text regions."""
+    if not settings.vision.enabled or not settings.vision.ocr.enabled:
+        return {'status': 'skipped', 'reason': 'OCR disabled'}
+    return asyncio.run(_ocr_photo_async(photo_id))
+
+
+async def _ocr_photo_async(photo_id: str):
+    image = _load_thumb(photo_id, "large")  # 1280px for better OCR accuracy
+    if image is None:
+        return {'status': 'error', 'message': 'thumbnail not found'}
+
+    from app.services.vision.registry import registry
+    ocr_engine = registry.get_ocr()
+    results = ocr_engine.run(image)
+
+    if not results:
+        logger.info("No OCR text found for photo %s", photo_id)
+        return {'status': 'success', 'photo_id': photo_id, 'regions': 0}
+
+    from app.models.ocr_text import OCRText
+
+    async with AsyncSessionLocal() as session:
+        # Delete existing OCR results for this photo (re-run safe)
+        await session.execute(
+            delete(OCRText).where(OCRText.photo_id == photo_id)
+        )
+        for r in results:
+            session.add(OCRText(
+                photo_id=photo_id,
+                text=r.text,
+                language=r.language,
+                confidence=r.confidence,
+                bbox=r.bbox,
+            ))
+        await session.commit()
+
+    logger.info("OCR: %d text regions for photo %s", len(results), photo_id)
+    return {'status': 'success', 'photo_id': photo_id, 'regions': len(results)}
 
 
 @shared_task(name='detect_objects', queue='vision')