fix(deploy): rework prod artifacts to match the actual Hetzner box

Server recon (read-only SSH) showed the box already runs ~8 apps behind a
host-level nginx, with Gitea + an Actions runner. The host-networking
design collided with contentra on port 3001.

- docker-compose.prod.yml: bridge networking + per-app network, house
  style; api/web/postgres/redis publish to 127.0.0.1 on verified-free
  ports (4000/4001/5440/6390); only the generator keeps host networking
  (no listening port, needs the host namespace for runner-port probing).
- Drop the Traefik config; the box uses a host nginx. Add a ready nginx
  vhost in infra/nginx/buildmymcpserver.conf (listen 80, Cloudflare TLS).
- Add .gitea/workflows/deploy.yml mirroring the buildmydiscord pipeline.
- Narrow the generated-MCP port range to 4400-4900 (clear of screencraft
  on 4321).
- .env.production.example + DEPLOY.md rewritten for buildmymcpserver.com
  and the real topology.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

infra/nginx/buildmymcpserver.conf

@@ -0,0 +1,68 @@
+# nginx vhost for buildmymcpserver.com — install on the host nginx:
+#   scp this to /etc/nginx/sites-available/buildmymcpserver
+#   ln -s /etc/nginx/sites-available/buildmymcpserver /etc/nginx/sites-enabled/
+#   nginx -t && systemctl reload nginx
+#
+# TLS is terminated by Cloudflare (proxied DNS records). The origin serves
+# plain HTTP on :80 — same pattern as the other Cloudflare-fronted apps here.
+# Set the Cloudflare SSL/TLS mode to "Full" for this zone.
+
+# --- Web app: buildmymcpserver.com ---
+server {
+    listen 80;
+    listen [::]:80;
+    server_name buildmymcpserver.com www.buildmymcpserver.com;
+
+    client_max_body_size 12M;
+
+    location / {
+        proxy_pass http://127.0.0.1:4001;
+        proxy_http_version 1.1;
+        proxy_set_header Upgrade $http_upgrade;
+        proxy_set_header Connection 'upgrade';
+        proxy_set_header Host $host;
+        proxy_set_header X-Real-IP $remote_addr;
+        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
+        proxy_set_header X-Forwarded-Proto $scheme;
+        proxy_cache_bypass $http_upgrade;
+        proxy_read_timeout 120s;
+    }
+}
+
+# --- Control plane API: api.buildmymcpserver.com ---
+server {
+    listen 80;
+    listen [::]:80;
+    server_name api.buildmymcpserver.com;
+
+    client_max_body_size 12M;
+
+    # Build-log WebSocket stream (/v1/builds/:id/stream) — needs the upgrade
+    # headers and a long read timeout; buffering off so frames are not held.
+    location /v1/builds/ {
+        proxy_pass http://127.0.0.1:4000;
+        proxy_http_version 1.1;
+        proxy_set_header Upgrade $http_upgrade;
+        proxy_set_header Connection 'upgrade';
+        proxy_set_header Host $host;
+        proxy_set_header X-Real-IP $remote_addr;
+        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
+        proxy_set_header X-Forwarded-Proto $scheme;
+        proxy_buffering off;
+        proxy_cache off;
+        proxy_read_timeout 600s;
+    }
+
+    location / {
+        proxy_pass http://127.0.0.1:4000;
+        proxy_http_version 1.1;
+        proxy_set_header Upgrade $http_upgrade;
+        proxy_set_header Connection 'upgrade';
+        proxy_set_header Host $host;
+        proxy_set_header X-Real-IP $remote_addr;
+        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
+        proxy_set_header X-Forwarded-Proto $scheme;
+        proxy_cache_bypass $http_upgrade;
+        proxy_read_timeout 120s;
+    }
+}