Remove w_uploads.storage_driver and route all read/write/delete paths through
storage.Active() backed by storage_config.driver. Block direct driver switches
when uploads exist; require migration task instead. Simplify migration to
cursor-based file_path iteration without per-row driver updates.
- Add access_mode column to w_uploads table (0 = private, 1 = public) and initialize data in a single migration script
- Enforce strict ownership check for private files during download
- Allow public files to follow whitelisted public-access rules
- Default access_mode to public for avatars and private for generic uploads
- Update frontend service to support optional accessMode parameter
ryan