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/audit.service.ts

@@ -25,6 +25,25 @@ export class FederationAuditService {
     });
   }
 
+  /**
+   * Log instance configuration update (system-level operation)
+   * Logged to application logs for security audit trail
+   */
+  logInstanceConfigurationUpdate(
+    userId: string,
+    instanceId: string,
+    updates: Record<string, unknown>
+  ): void {
+    this.logger.log({
+      event: "FEDERATION_INSTANCE_CONFIG_UPDATED",
+      userId,
+      instanceId,
+      updates,
+      timestamp: new Date().toISOString(),
+      securityEvent: true,
+    });
+  }
+
   /**
    * Log federated authentication initiation
    */