Improve file listing and fix notification metadata field

Backend:
- Optimize file listing for non-superusers with dedicated CRUD methods
- Add get_visible_for_user and count_visible_for_user for efficient queries
- Move /allowed-types/ and /max-size/ routes before /{file_id} for proper matching
- Rename notification 'metadata' field to 'extra_data' for clarity
- Fix settings export to use get_value() method

Frontend:
- Update NotificationItem interface to use extra_data field

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/app/api/v1/files.py

@@ -137,57 +137,53 @@ def list_files(
     # Filter by ownership for non-superusers
     if not current_user.is_superuser:
         if mine_only:
-            uploaded_by = current_user.id
-            is_public = None
+            files = crud.file_storage.get_multi(
+                db,
+                skip=skip,
+                limit=page_size,
+                uploaded_by=current_user.id,
+                is_public=is_public,
+                content_type=content_type
+            )
+            total = crud.file_storage.count(
+                db,
+                uploaded_by=current_user.id,
+                is_public=is_public,
+                content_type=content_type
+            )
         else:
-            # Show user's files and public files
-            own_files = crud.file_storage.get_multi(
+            files = crud.file_storage.get_visible_for_user(
                 db,
-                skip=0,
-                limit=1000,  # Get all for filtering
-                uploaded_by=current_user.id
+                user_id=current_user.id,
+                skip=skip,
+                limit=page_size,
+                is_public=is_public,
+                content_type=content_type
             )
-            public_files = crud.file_storage.get_multi(
+            total = crud.file_storage.count_visible_for_user(
                 db,
-                skip=0,
-                limit=1000,
-                is_public=True
+                user_id=current_user.id,
+                is_public=is_public,
+                content_type=content_type
             )
-            # Combine and deduplicate
-            all_files = {f.id: f for f in own_files}
-            all_files.update({f.id: f for f in public_files})
-            files_list = list(all_files.values())
-            # Sort by created_at desc
-            files_list.sort(key=lambda x: x.created_at, reverse=True)
-            # Paginate
-            total = len(files_list)
-            files = files_list[skip:skip + page_size]
-
-            return {
-                "files": [file_to_schema(f) for f in files],
-                "total": total,
-                "page": page,
-                "page_size": page_size
-            }
-
-        uploaded_by = current_user.id if mine_only else None
     else:
         uploaded_by = current_user.id if mine_only else None
 
-    files = crud.file_storage.get_multi(
-        db,
-        skip=skip,
-        limit=page_size,
-        uploaded_by=uploaded_by,
-        is_public=is_public,
-        content_type=content_type
-    )
+        files = crud.file_storage.get_multi(
+            db,
+            skip=skip,
+            limit=page_size,
+            uploaded_by=uploaded_by,
+            is_public=is_public,
+            content_type=content_type
+        )
 
-    total = crud.file_storage.count(
-        db,
-        uploaded_by=uploaded_by,
-        is_public=is_public
-    )
+        total = crud.file_storage.count(
+            db,
+            uploaded_by=uploaded_by,
+            is_public=is_public,
+            content_type=content_type
+        )
 
     return {
         "files": [file_to_schema(f) for f in files],
@@ -197,6 +193,29 @@ def list_files(
     }
 
 
+@router.get("/allowed-types/", response_model=List[str])
+def get_allowed_types(
+    current_user: User = Depends(get_current_user),
+):
+    """
+    Get list of allowed file types for upload.
+    """
+    return ALLOWED_CONTENT_TYPES
+
+
+@router.get("/max-size/", response_model=dict)
+def get_max_size(
+    current_user: User = Depends(get_current_user),
+):
+    """
+    Get maximum allowed file size.
+    """
+    return {
+        "max_size_bytes": MAX_FILE_SIZE,
+        "max_size_mb": MAX_FILE_SIZE / (1024 * 1024)
+    }
+
+
 @router.get("/{file_id}", response_model=StoredFileSchema)
 def get_file(
     file_id: str,
@@ -352,26 +371,3 @@ def delete_file(
         crud.file_storage.soft_delete(db, id=file_id)
 
     return None
-
-
-@router.get("/allowed-types/", response_model=List[str])
-def get_allowed_types(
-    current_user: User = Depends(get_current_user),
-):
-    """
-    Get list of allowed file types for upload.
-    """
-    return ALLOWED_CONTENT_TYPES
-
-
-@router.get("/max-size/", response_model=dict)
-def get_max_size(
-    current_user: User = Depends(get_current_user),
-):
-    """
-    Get maximum allowed file size.
-    """
-    return {
-        "max_size_bytes": MAX_FILE_SIZE,
-        "max_size_mb": MAX_FILE_SIZE / (1024 * 1024)
-    }