feat(M002): smart playlists — rule engine, editor UI, sidebar integration

Recovered from orphaned worktree commits (complete-milestone failed to merge).

Backend:
- Migration 9: is_smart + smart_rules columns on playlists table
- smartplaylist package: parameterized WHERE clause builder, field whitelist, genre subquery
- playlist.Service: Create/Update/Evaluate/Preview/GetRules smart playlist methods
- 65 tests (49 rule engine + 15 service + 1 migration)

Frontend:
- yj-combobox: reusable typeable dropdown with keyboard nav, ARIA, blur-race fix
- smart-playlist-editor: row-based rule builder with live preview
- smart-playlist-details: evaluate, refresh, play, shuffle, edit rules
- Sidebar: filter icon, Smart badge, create button, routing
- Queue snapshot on play/shuffle

frontend/wailsjs/go/models.ts

@@ -483,6 +483,7 @@ export namespace playlist {
 	    Name: string;
 	    CreatedAt: string;
 	    UpdatedAt: string;
+	    IsSmart: boolean;
 	
 	    static createFrom(source: any = {}) {
 	        return new Summary(source);
@@ -494,6 +495,7 @@ export namespace playlist {
 	        this.Name = source["Name"];
 	        this.CreatedAt = source["CreatedAt"];
 	        this.UpdatedAt = source["UpdatedAt"];
+	        this.IsSmart = source["IsSmart"];
 	    }
 	}
 	export class Track {