fix(render): remove broken fromDatabase reference for WMG_DB_URL

The render.yaml had a fromDatabase reference to worldmodel-gym-db
(paid plan basic-256mb) that was never provisioned through the
blueprint. This caused WMG_DB_URL to resolve to an empty string,
crashing the app on startup (exit status 3).

Changes:
- Remove databases section (DB managed manually via Render dashboard)
- Remove fromDatabase WMG_DB_URL (set manually with credentials)
- Add WMG_LEGACY_UPLOAD_TOKEN_ENABLED=false to disable legacy auth

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: biru-codeastromer

render.yaml

@@ -1,7 +1,3 @@
-databases:
-  - name: worldmodel-gym-db
-    plan: basic-256mb
-
 services:
   - type: web
     name: worldmodel-gym-api
@@ -14,10 +10,8 @@ services:
     envVars:
       - key: WMG_ENV
         value: production
-      - key: WMG_DB_URL
-        fromDatabase:
-          name: worldmodel-gym-db
-          property: connectionString
+      # WMG_DB_URL is set manually in the Render dashboard
+      # (contains credentials — not stored in git)
       - key: WMG_AUTO_MIGRATE
         value: "true"
       - key: WMG_STORAGE_DIR
@@ -28,5 +22,7 @@ services:
         value: "true"
       - key: WMG_CORS_ORIGINS
         value: https://world-model-gym.vercel.app
+      - key: WMG_LEGACY_UPLOAD_TOKEN_ENABLED
+        value: "false"
       - key: WMG_UPLOAD_TOKEN
         generateValue: true