Feature 24: commit the admin PWA hosting artifacts and runbook section

Make the live admin PWA deployment reproducible from the repository:

- deploy/pwa/Dockerfile: multi-stage build (node:22-alpine builds admin/
  with the VITE_* build args, failing fast if any is empty; nginx:alpine
  pinned to the digest running on the API box serves dist/).
- deploy/pwa/Dockerfile.dockerignore: limits the repo-root context to
  admin/ sources and nginx.conf (the root .dockerignore excludes deploy/).
- deploy/pwa/nginx.conf: SPA fallback to index.html, root-served
  /sw.js and /manifest.webmanifest, allow-list 10.60.1.33 and
  10.60.1.14 only.
- deploy/compose.yaml: pwa service on NESTQUEST_BIND_ADDRESS:8081 with
  the build args from deploy/.env; api and litestream unchanged.
- deploy/.env.example: the three public PWA build values.
- deploy/RUNBOOK.md: section 10 (PWA build/serve, nestquest-app Traefik
  router, verification) and the router priorities in section 3.

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

deploy/pwa/nginx.conf

@@ -0,0 +1,53 @@
+# nginx server for the NestQuest admin PWA (Feature 24).  Replaces the
+# image's /etc/nginx/conf.d/default.conf.  The shared Traefik on
+# nukapi-03 (10.60.1.33) terminates TLS for nestquest.cubecraftlabs.com
+# and forwards every path that is not the API (/api, /health,
+# /openapi.json, /docs) here; see deploy/RUNBOOK.md section 10.
+server {
+    listen 80;
+    server_name _;
+
+    # Only the reverse proxy and the API box itself may connect; every
+    # other source is refused (403) even if the port is reachable.
+    allow 10.60.1.33;
+    allow 10.60.1.14;
+    deny all;
+
+    root /usr/share/nginx/html;
+    index index.html;
+    server_tokens off;
+
+    # Content-hashed bundle files: cache forever, and a missing asset is
+    # a real 404 rather than the SPA shell.
+    location /assets/ {
+        try_files $uri =404;
+        add_header Cache-Control "public, max-age=31536000, immutable";
+    }
+
+    # The service worker must be revalidated on every load so a new
+    # release's worker (fresh revision, see admin/vite-sw-plugin.ts) is
+    # picked up.
+    location = /sw.js {
+        try_files $uri =404;
+        add_header Cache-Control "no-cache";
+    }
+
+    # nginx's stock mime.types has no .webmanifest entry.
+    location = /manifest.webmanifest {
+        types { }
+        default_type application/manifest+json;
+        try_files $uri =404;
+        add_header Cache-Control "no-cache";
+    }
+
+    # SPA fallback: client routes such as /auth/callback resolve to the
+    # app shell, which is never cached so it always names the current
+    # hashed assets.
+    location / {
+        try_files $uri $uri/ /index.html;
+    }
+
+    location = /index.html {
+        add_header Cache-Control "no-cache";
+    }
+}