fix: address code review findings from 2026-08-17

- scope no-cache headers to non-static routes (restore immutable asset caching)
- reset cached rejected MongoDB promise so retries can succeed
- use last X-Forwarded-For entry in Content Editor rate limiter (anti-spoofing)
- remove weak Mongo defaults from compose files (fail loudly on missing env)
- move staging banner text to common.json content
- read APP_PORT from env file in deploy.sh healthcheck
- filter network noise from staging smoke console assertions

Closes MITHOME-48, MITHOME-49, MITHOME-50, MITHOME-51, MITHOME-52, MITHOME-53, MITHOME-54

proto/src/content/common.json

@@ -13,5 +13,8 @@
     "required": "Ez a mező kötelező",
     "invalidEmail": "Érvénytelen email cím formátum",
     "minLength": "Legalább {min} karakter szükséges"
+  },
+  "staging": {
+    "banner": "⚠ STAGING / TESZTKÖRNYEZET — A STAGING OLDALT LÁTOD"
   }
 }