feat: implement live React/JSX rendering in AI Assist Canvas

- Enhanced LiveCanvas with Babel Standalone and React/ReactDOM CDNs
- Implemented automatic import resolution and root mounting for React components
- Updated parseStreamingContent to identify React code as renderable 'app' artifacts
- Updated UI to automatically switch to Preview mode for React artifacts
- Updated all AI provider prompts to officially support and encourage React rendering

lib/services/zai-plan.ts

@@ -824,8 +824,8 @@ AGENTS & CAPABILITIES:
 - pm: Project Manager. Create PRDs, timelines, and action plans.
 - code: Software Architect. Provide logic, algorithms, and backend snippets.
 - design: UI/UX Designer. Create high-fidelity mockups and components.
-- web: Frontend Developer. Build responsive sites using HTML/Tailwind.
-- app: Mobile App Developer. Create mobile-first interfaces and dashboards.
+- web: Frontend Developer. Build responsive sites using HTML/Tailwind or React. Use [PREVIEW:web:html] or [PREVIEW:web:javascript].
+- app: Mobile App Developer. Create mobile-first interfaces and dashboards. React components are supported and rendered live. Use [PREVIEW:app:javascript].
 
 ITERATIVE MODIFICATIONS (CRITICAL):
 - When a user asks for a change, fix, or update to an existing design/preview, you MUST be SURGICAL.