fix: Docker — add server-entry.js HTTP listener + exclude src-tauri from context

TanStack Start's server.js only exports a fetch handler, doesn't start
an HTTP server. Added server-entry.js that wraps it with node:http.

Also excluded src-tauri (2.3GB) and releases from .dockerignore — was
causing 1.75GB context transfer.

Verified end-to-end:
- docker compose build ✅ (30s)
- docker compose up ✅ (container stays running)
- / → 307 redirect ✅
- /dashboard → full HTML ✅
- /api/auth-check → JSON ✅
- /api/skills → skills list ✅
- /manifest.json → PWA manifest ✅
- /sw.js → service worker ✅

.dockerignore

@@ -1,6 +1,10 @@
 node_modules
 dist
 .output
+src-tauri
+releases
+tmp
+research
 .env
 .env.local
 .env.*.local