feat(ai): assistant panel, AI settings and studio generator UI

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

apps/web/src/features.ts

@@ -2,3 +2,4 @@ import type { WebFeature } from "@stc/contracts";
 
 // Phase 1 packages append one import line each and push into this list.
 export const webFeatures: WebFeature[] = [];
+import { aiWeb } from "../../../packages/feature-ai/src/web"; webFeatures.push(aiWeb);