Harden template for production: add comments, fix bugs, add lock file

- Add inline comments to docker-compose.yml explaining the 5 key rules
  (expose vs ports, DB host, DB name persistence, no Traefik labels)
- Add comments to Dockerfile explaining multi-stage build, layer caching,
  and why .dockerignore excludes client/dist
- Add comments to .dockerignore explaining each exclusion
- Fix dev script: use nodemon (auto-restart) instead of node for server.js
- Add postinstall script to auto-install client deps (cd client && npm install)
- Fix SPA fallback: bare return → next() to prevent hanging requests
- Add root package-lock.json for deterministic server dependency installs
- Remove committed tsconfig.tsbuildinfo build artifact, add *.tsbuildinfo to .gitignore
- Update README: simpler install (npm install handles everything), reference SAAC_DEPLOYMENT.md,
  use npx instead of pnpm dlx for shadcn components

package.json

@@ -5,8 +5,9 @@
   "main": "server.js",
   "scripts": {
     "start": "node server.js",
-    "dev": "concurrently \"node server.js\" \"cd client && npm run dev\"",
+    "dev": "concurrently \"nodemon server.js\" \"cd client && npm run dev\"",
     "build": "cd client && npm run build",
+    "postinstall": "[ -d client ] && cd client && npm install || true",
     "dev:server": "nodemon server.js",
     "dev:client": "cd client && npm run dev"
   },