feat(#94): implement spoke configuration UI

Implements the final piece of M7-Federation - the spoke configuration UI
that allows administrators to configure their local instance's federation
capabilities and settings.

Backend Changes:
- Add UpdateInstanceDto with validation for name, capabilities, and metadata
- Implement FederationService.updateInstanceConfiguration() method
- Add PATCH /api/v1/federation/instance endpoint to FederationController
- Add audit logging for configuration updates
- Add tests for updateInstanceConfiguration (5 new tests, all passing)

Frontend Changes:
- Create SpokeConfigurationForm component with PDA-friendly design
- Create /federation/settings page with configuration management
- Add regenerate keypair functionality with confirmation dialog
- Extend federation API client with updateInstanceConfiguration and regenerateInstanceKeys
- Add comprehensive tests (10 tests, all passing)

Design Decisions:
- Admin-only access via AdminGuard
- Never expose private key in API responses (security)
- PDA-friendly language throughout (no demanding terms)
- Clear visual hierarchy with read-only and editable fields
- Truncated public key with copy button for usability
- Confirmation dialog for destructive key regeneration

All tests passing:
- Backend: 13/13 federation service tests passing
- Frontend: 10/10 SpokeConfigurationForm tests passing
- TypeScript compilation: passing
- Linting: passing
- PDA-friendliness: verified

This completes M7-Federation. All federation features are now implemented.

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

apps/api/src/federation/federation.controller.spec.ts

@@ -8,6 +8,7 @@ import { FederationController } from "./federation.controller";
 import { FederationService } from "./federation.service";
 import { FederationAuditService } from "./audit.service";
 import { ConnectionService } from "./connection.service";
+import { FederationAgentService } from "./federation-agent.service";
 import { AuthGuard } from "../auth/guards/auth.guard";
 import { AdminGuard } from "../auth/guards/admin.guard";
 import { FederationConnectionStatus } from "@prisma/client";
@@ -88,6 +89,14 @@ describe("FederationController", () => {
             handleIncomingConnectionRequest: vi.fn(),
           },
         },
+        {
+          provide: FederationAgentService,
+          useValue: {
+            spawnAgentOnRemote: vi.fn(),
+            getAgentStatus: vi.fn(),
+            killAgentOnRemote: vi.fn(),
+          },
+        },
       ],
     })
       .overrideGuard(AuthGuard)