feat(server): serve the client-only build with Bun

Angular's server build needs Node loader hooks that Bun does not apply,
and every route is client-rendered, so Angular now builds a client-only
bundle and a small Bun.serve server delivers it: hashed assets with the
one-year cache, index.html revalidated, extension-less routes falling
back to index.html, missing assets 404, traversal and malformed paths
rejected, and other methods 405. Express, @angular/ssr and the unused
hydration provider are removed. Both Docker stages use the pinned
oven/bun:1.4.3-alpine image without Node, and the health checks use
Bun's fetch.

Refs #292

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

compose.prod.yml

@@ -17,7 +17,7 @@ services:
                     'CMD',
                     'bun',
                     '-e',
-                    "require('http').get('http://localhost:4000', (r) => {process.exit(r.statusCode === 200 ? 0 : 1)})",
+                    "fetch('http://localhost:4000/').then(r => process.exit(r.ok ? 0 : 1), () => process.exit(1))",
                 ]
             interval: 30s
             timeout: 10s