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/dto/instance.dto.ts

@@ -0,0 +1,46 @@
+/**
+ * Instance Configuration DTOs
+ *
+ * Data Transfer Objects for instance configuration API.
+ */
+
+import { IsString, IsBoolean, IsOptional, IsObject, ValidateNested } from "class-validator";
+import { Type } from "class-transformer";
+
+/**
+ * DTO for federation capabilities
+ */
+export class FederationCapabilitiesDto {
+  @IsBoolean()
+  supportsQuery!: boolean;
+
+  @IsBoolean()
+  supportsCommand!: boolean;
+
+  @IsBoolean()
+  supportsEvent!: boolean;
+
+  @IsBoolean()
+  supportsAgentSpawn!: boolean;
+
+  @IsString()
+  protocolVersion!: string;
+}
+
+/**
+ * DTO for updating instance configuration
+ */
+export class UpdateInstanceDto {
+  @IsOptional()
+  @IsString()
+  name?: string;
+
+  @IsOptional()
+  @ValidateNested()
+  @Type(() => FederationCapabilitiesDto)
+  capabilities?: FederationCapabilitiesDto;
+
+  @IsOptional()
+  @IsObject()
+  metadata?: Record<string, unknown>;
+}