feat: Implement directory browsing functionality

- Add `browseDirectory` API endpoint to list directory contents.
- Create `FolderBrowser` component for user interface to navigate directories.
- Update `Scan` page to integrate folder browsing feature.
- Define `DirectoryItem` and `BrowseDirectoryResponse` schemas for API responses.

backend/schemas/photos.py

@@ -91,3 +91,20 @@ class BulkDeletePhotosResponse(BaseModel):
         description="Photo IDs that were requested but not found",
     )
 
+
+class DirectoryItem(BaseModel):
+    """Directory item (file or folder) in a directory listing."""
+
+    name: str = Field(..., description="Name of the item")
+    path: str = Field(..., description="Full absolute path to the item")
+    is_directory: bool = Field(..., description="Whether this is a directory")
+    is_file: bool = Field(..., description="Whether this is a file")
+
+
+class BrowseDirectoryResponse(BaseModel):
+    """Response for directory browsing."""
+
+    current_path: str = Field(..., description="Current directory path")
+    parent_path: Optional[str] = Field(None, description="Parent directory path (None if at root)")
+    items: List[DirectoryItem] = Field(..., description="List of items in the directory")
+