feat: integrate auto-photo-save into item creation endpoint

- Extend ItemCreate schema with optional extracted_image_bytes (base64) and image_processing (dict)
- Update create_item endpoint to call _auto_save_photo_from_extraction after item creation
- Decode base64 image bytes and pass crop_bounds, rotation_degrees to helper
- Don't block item creation if photo save fails (log warning instead)
- Item returned with photo_path, photo_thumbnail_path populated if save succeeded
- Full backward compatibility: old clients without image fields work unchanged
- Add 5 integration tests covering all scenarios:
  - Create item WITH image_processing → photo auto-saved
  - Create item WITHOUT image_processing → no photo (backward compatible)
  - Create item WITH invalid image_processing → item created, photo skipped
  - Create item WITH crop_bounds=None → item created, photo skipped
  - Create item WITH bytes but NO processing metadata → item created, photo skipped
- All 158 backend tests passing, zero regressions

backend/routers/items.py

@@ -140,11 +140,37 @@ def create_item(
             db.add(models.Color(name=item.color))
             db.commit()
 
-    db_item = models.Item(**item.model_dump())
+    # Exclude image_processing fields from database item creation (backward compatible)
+    item_data = item.model_dump(exclude={"extracted_image_bytes", "image_processing"})
+    db_item = models.Item(**item_data)
     db.add(db_item)
     db.commit()
     db.refresh(db_item)
 
+    # NEW: Auto-save photo if extracted_image_bytes and image_processing provided
+    if item.extracted_image_bytes and item.image_processing:
+        try:
+            import base64
+            image_bytes = base64.b64decode(item.extracted_image_bytes)
+
+            photo_result = _auto_save_photo_from_extraction(
+                item_id=db_item.id,
+                image_bytes=image_bytes,
+                crop_bounds=item.image_processing.get("crop_bounds"),
+                rotation_degrees=item.image_processing.get("rotation_degrees", 0),
+                db=db
+            )
+
+            if photo_result["status"] == "ok":
+                db.refresh(db_item)  # Reload to get updated photo fields
+            else:
+                from ..logger import log
+                log.warning(f"Photo auto-save skipped for item {db_item.id}: {photo_result.get('reason')}")
+        except Exception as e:
+            from ..logger import log
+            log.error(f"Exception during auto-save for item {db_item.id}: {e}")
+            # Don't fail item creation
+
     # Audit log the creation — [M-02] user_id from token, not from body
     # Capture full snapshot
     item_snapshot = {