fix(#290): Secure identity verification endpoint

Added @UseGuards(AuthGuard) and rate limiting (@Throttle) to
/api/v1/federation/identity/verify endpoint. Configured strict
rate limit (10 req/min) to prevent abuse of this previously
public endpoint. Added test to verify guards are applied.

Security improvement: Prevents unauthorized access and rate limit
abuse of identity verification endpoint.

Fixes #290

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

apps/api/src/federation/identity-linking.controller.spec.ts

@@ -90,6 +90,15 @@ describe("IdentityLinkingController", () => {
   });
 
   describe("POST /identity/verify", () => {
+    it("should have AuthGuard and Throttle decorators applied", () => {
+      // Verify that the endpoint has proper guards and rate limiting
+      const verifyMetadata = Reflect.getMetadata(
+        "__guards__",
+        IdentityLinkingController.prototype.verifyIdentity
+      );
+      expect(verifyMetadata).toBeDefined();
+    });
+
     it("should verify identity with valid request", async () => {
       const dto: VerifyIdentityDto = {
         localUserId: "local-user-id",