fix(api): make federation config validation non-fatal at startup

Federation is optional and should not prevent the app from starting
when DEFAULT_WORKSPACE_ID is not set. Changed from throwing (crash)
to logging a warning. The endpoint-level validation in the controller
still rejects requests when federation is unconfigured.

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

apps/api/src/federation/federation.module.ts

@@ -99,10 +99,9 @@ export class FederationModule implements OnModuleInit {
       validateFederationConfig();
       this.logger.log("Federation configuration validated successfully");
     } catch (error) {
-      this.logger.error(
-        `Federation configuration validation failed: ${error instanceof Error ? error.message : String(error)}`
+      this.logger.warn(
+        `Federation disabled: ${error instanceof Error ? error.message : String(error)}`
       );
-      throw error;
     }
   }
 }