Add SSR bridge: Django template backend + Bun subprocess renderer

Mizan's SSR is a Django template backend. Configure in TEMPLATES:

    TEMPLATES = [{
        'BACKEND': 'mizan.ssr.MizanTemplates',
        'OPTIONS': {'worker_path': 'frontend/ssr-worker.tsx'},
    }]

Then render(request, 'ProfilePage', {'user_id': 5}) renders the React
component via a persistent Bun subprocess. The component name is the
template name. The context dict becomes props.

Architecture:
- Bun worker: stdin/stdout JSON-RPC, renderToString, component registry
- Django bridge: subprocess lifecycle, crash recovery, concurrent renders
- Template backend: implements Django's BaseEngine interface

This is the AFI's SSR boundary:
- Backend adapter implements mizan.ssr() (data gathering)
- Frontend adapter implements renderToHTML() (component rendering)
- Bun subprocess is the runtime hosting the frontend adapter

11 tests: ping, render, error handling, crash recovery, concurrent
renders (5 threads), template backend integration. All require Bun.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/mizan-ssr/src/index.ts

@@ -0,0 +1 @@
+export { registerComponent } from './worker'