feat(settings): runtime log level + free provider enable/disable

- Add LOG_LEVEL env + runtime setLogLevel (dashboard Settings → Logging),
  applied immediately, persisted across restarts; WARN/ERROR quiet production
  INFO lines (▶ POST / 📊 DONE / [COMBO] / [CHAT])
- Allow toggling free/noAuth providers (gemini-cli, kilo, etc.) off via
  providerStrategies.enabled from Providers page and provider detail page
- auth.js: honor disabled override before noAuth/connection branches
- CompatibleModelsSection: parallel model testing

.env.example

@@ -14,6 +14,10 @@ NODE_ENV=production
 API_KEY_SECRET=endpoint-proxy-api-key-secret
 MACHINE_ID_SALT=endpoint-proxy-salt
 ENABLE_REQUEST_LOGS=false
+# Console verbosity: DEBUG | INFO | WARN | ERROR. Default INFO. In production set
+# ERROR to only print important errors (hides ▶ POST / 📊 DONE / [COMBO] / [CHAT]).
+# Can also be changed at runtime from dashboard Settings → Logging.
+# LOG_LEVEL=ERROR
 OBSERVABILITY_ENABLED=true
 AUTH_COOKIE_SECURE=false
 REQUIRE_API_KEY=false