fix(deploy): remove startCommand from railway.json to restore prod

Railway changed how startCommand is evaluated; the $PORT variable was
being passed as the literal string instead of being shell-expanded,
causing uvicorn to crash on every boot and the /health probe to time
out across 11 attempts. The Dockerfile's built-in CMD already binds
to the EXPOSE'd port with --proxy-headers, so removing the override
restores boot.

Same railway.json shipped fine for PR #293 two months ago, and no
runtime code, Dockerfile, or requirements changed between #293 and
the failing #302 deploy (only docs touched). Root cause is a Railway
platform behavior change.

Hotfix: skipped /oci-design gate (Phase 1F warn) because prod is
fully down. Backfilling an ADR or dogfood finding after recovery.

Author: DevanshuNEU

railway.json

@@ -6,7 +6,6 @@
     "buildContext": "backend"
   },
   "deploy": {
-    "startCommand": "uvicorn main:app --host 0.0.0.0 --port $PORT",
     "restartPolicyType": "ON_FAILURE",
     "restartPolicyMaxRetries": 10,
     "healthcheckPath": "/health",