Add mkdir and mv (rename) FUSE operations to the virtual filesystem:
- mkdir: Create directories that persist across remounts via SQLite
- mv: Move/rename files and directories with database persistence
Changes:
- Add directories table to schema for user-created empty dirs
- Add tree operations: mkdir, rename_file, rename_directory
- Add DB methods for path updates and directory CRUD
- Remove MountOption::RO to allow write syscalls
- Load stored virtual_path from DB instead of regenerating
- Restore user directories on mount from directories table
- Upsert files to DB during origin scan
POSIX compliant: mv fails with ENOENT if parent doesn't exist
(use mkdir first, shell handles -p flag and brace expansion)
Alexander