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/crud/file.py

@@ -9,6 +9,7 @@ from datetime import datetime
 from pathlib import Path
 from typing import Optional, List, BinaryIO
 from sqlalchemy.orm import Session
+from sqlalchemy import or_
 
 from app.models.file import StoredFile
 from app.schemas.file import FileCreate, FileUpdate, ALLOWED_CONTENT_TYPES, MAX_FILE_SIZE
@@ -132,12 +133,36 @@ class CRUDFile:
 
         return query.order_by(StoredFile.created_at.desc()).offset(skip).limit(limit).all()
 
+    def get_visible_for_user(
+        self,
+        db: Session,
+        *,
+        user_id: str,
+        skip: int = 0,
+        limit: int = 100,
+        is_public: Optional[bool] = None,
+        content_type: Optional[str] = None
+    ) -> List[StoredFile]:
+        """Get files visible to a user (own + public) with optional filtering."""
+        query = db.query(StoredFile).filter(
+            StoredFile.is_deleted == False,
+            or_(StoredFile.uploaded_by == user_id, StoredFile.is_public == True)
+        )
+
+        if is_public is not None:
+            query = query.filter(StoredFile.is_public == is_public)
+        if content_type:
+            query = query.filter(StoredFile.content_type.like(f"{content_type}%"))
+
+        return query.order_by(StoredFile.created_at.desc()).offset(skip).limit(limit).all()
+
     def count(
         self,
         db: Session,
         *,
         uploaded_by: Optional[str] = None,
-        is_public: Optional[bool] = None
+        is_public: Optional[bool] = None,
+        content_type: Optional[str] = None
     ) -> int:
         """Count files with optional filtering."""
         query = db.query(StoredFile).filter(StoredFile.is_deleted == False)
@@ -146,9 +171,31 @@ class CRUDFile:
             query = query.filter(StoredFile.uploaded_by == uploaded_by)
         if is_public is not None:
             query = query.filter(StoredFile.is_public == is_public)
+        if content_type:
+            query = query.filter(StoredFile.content_type.like(f"{content_type}%"))
 
         return query.count()
 
+    def count_visible_for_user(
+        self,
+        db: Session,
+        *,
+        user_id: str,
+        is_public: Optional[bool] = None,
+        content_type: Optional[str] = None
+    ) -> int:
+        """Count files visible to a user (own + public) with optional filtering."""
+        query = db.query(StoredFile).filter(
+            StoredFile.is_deleted == False,
+            or_(StoredFile.uploaded_by == user_id, StoredFile.is_public == True)
+        )
+
+        if is_public is not None:
+            query = query.filter(StoredFile.is_public == is_public)
+        if content_type:
+            query = query.filter(StoredFile.content_type.like(f"{content_type}%"))
+
+        return query.count()
     def create(
         self,
         db: Session,