Drop the read-only cache + SD Uploader design in favor of rclone VFS
native read-write caching. Key changes:
- SMB shares are now read-write, writes go to SSD and async write-back to NAS
- Remove SD card import/upload, metadata DB, self-built polling
- Simplify remote change detection to rclone --dir-cache-time
- Add dirty file management, write-back config, and related risks
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
