chore: serve everything on port 1337

User-facing port unified at 1337 — vibes-aligned and easier to remember
than 8080/8420. Updates: api default PORT, .env.example, docker-compose
mapping (1337:1337), healthcheck target, Dockerfile EXPOSE, Vite dev
proxy.

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

.env.example

@@ -2,7 +2,7 @@
 # Copy to .env (or set in Portainer stack env) and fill in values.
 
 # ---- Server ----
-PORT=8080
+PORT=1337
 NODE_ENV=production
 LOG_LEVEL=info
 # Origin allowed by CORS. Leave unset to disable CORS entirely (single-origin