feat: Visual CoPilot module + collapsible sidebar

- Add visual-copilot module (iframe embed, env: NEXT_PUBLIC_VIM_URL)
- Sidebar collapse to icon-only with localStorage persistence
- Tooltips on collapsed nav items
- Full-viewport layout for canvas routes (/visual-copilot)
- Register module in modules.ts + feature flag in flags.ts

src/modules/visual-copilot/index.ts

@@ -0,0 +1,2 @@
+export { VisualCopilotModule } from "./components/visual-copilot-module";
+export { visualCopilotConfig } from "./config";