PlaylistProvider capability now requires 'users' permission in the
manifest (matching existing Scrobbler behavior) and validates that the
resolved owner user ID is in the plugin's allowed users list before
creating playlists.
Rename the capability from PlaylistGenerator to PlaylistProvider and the
internal orchestrator struct from playlistGeneratorOrchestrator to
playlistSyncer. The new names better describe what the capability does
(provides playlists) rather than how it works internally. All source
files, test plugin, PDK packages (Go/Rust), YAML schemas, and exported
WASM function names are updated accordingly.