feat(#93): implement agent spawn via federation

Implements FED-010: Agent Spawn via Federation feature that enables
spawning and managing Claude agents on remote federated Mosaic Stack
instances via COMMAND message type.

Features:
- Federation agent command types (spawn, status, kill)
- FederationAgentService for handling agent operations
- Integration with orchestrator's agent spawner/lifecycle services
- API endpoints for spawning, querying status, and killing agents
- Full command routing through federation COMMAND infrastructure
- Comprehensive test coverage (12/12 tests passing)

Architecture:
- Hub → Spoke: Spawn agents on remote instances
- Command flow: FederationController → FederationAgentService →
  CommandService → Remote Orchestrator
- Response handling: Remote orchestrator returns agent status/results
- Security: Connection validation, signature verification

Files created:
- apps/api/src/federation/types/federation-agent.types.ts
- apps/api/src/federation/federation-agent.service.ts
- apps/api/src/federation/federation-agent.service.spec.ts

Files modified:
- apps/api/src/federation/command.service.ts (agent command routing)
- apps/api/src/federation/federation.controller.ts (agent endpoints)
- apps/api/src/federation/federation.module.ts (service registration)
- apps/orchestrator/src/api/agents/agents.controller.ts (status endpoint)
- apps/orchestrator/src/api/agents/agents.module.ts (lifecycle integration)

Testing:
- 12/12 tests passing for FederationAgentService
- All command service tests passing
- TypeScript compilation successful
- Linting passed

Refs #93

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

docs/scratchpads/orch-115-dispatch.md

@@ -0,0 +1,99 @@
+# ORCH-115: Task dispatch from coordinator
+
+## Objective
+
+Implement orchestrator API endpoint POST /agents/spawn to receive spawn requests from coordinator, queue tasks in Valkey, and spawn agents.
+
+## Acceptance Criteria
+
+- [ ] Orchestrator API endpoint: POST /agents/spawn
+- [ ] Coordinator calls orchestrator after quality pre-check
+- [ ] Task queued in Valkey
+- [ ] Agent spawned
+- [ ] Return agentId to coordinator
+
+## Approach
+
+1. Create NestJS controller: `src/api/agents/agents.controller.ts`
+2. Create DTO for spawn request validation
+3. Integrate with QueueService (ORCH-108) and AgentSpawnerService (ORCH-105)
+4. Write comprehensive unit tests following TDD
+5. Create module and register in AppModule
+
+## API Specification
+
+```typescript
+POST /agents/spawn
+Request: {
+  taskId: string,
+  agentType: 'worker' | 'reviewer' | 'tester',
+  context: {
+    repository: string,
+    branch: string,
+    workItems: string[],
+    skills?: string[]
+  }
+}
+Response: {
+  agentId: string,
+  status: 'spawning' | 'queued'
+}
+```
+
+## Progress
+
+- [x] Write controller tests (RED)
+- [x] Implement controller (GREEN)
+- [x] Refactor if needed
+- [x] Create module
+- [x] Register in AppModule
+- [x] Integration test
+- [x] Add class-validator and class-transformer dependencies
+- [x] All tests passing (14/14)
+- [x] Test coverage 100%
+
+## Testing Strategy
+
+- Mock QueueService.addTask()
+- Mock AgentSpawnerService.spawnAgent()
+- Test success scenarios
+- Test validation errors (missing fields, invalid types)
+- Test service integration errors
+- Ensure coverage >= 85%
+
+## Notes
+
+- Following existing patterns from health.controller.ts
+- Using NestJS dependency injection
+- DTOs will validate request payload
+- Return agentId from spawner service
+- Queue status reflects whether agent is spawning or queued
+
+## Implementation Summary
+
+### Files Created:
+
+1. `src/api/agents/agents.controller.ts` - Main controller with POST /agents/spawn endpoint
+2. `src/api/agents/agents.controller.spec.ts` - Comprehensive unit tests (14 tests, 100% coverage)
+3. `src/api/agents/dto/spawn-agent.dto.ts` - Request/response DTOs with validation
+4. `src/api/agents/agents.module.ts` - NestJS module
+
+### Files Modified:
+
+1. `src/app.module.ts` - Added AgentsModule import
+2. `package.json` - Added class-validator and class-transformer dependencies
+
+### Test Results:
+
+- All 238 tests passing
+- Controller tests: 14/14 passing
+- Coverage: 100% (statements, branches, functions, lines)
+
+### Key Features:
+
+- Spawns agents using AgentSpawnerService
+- Queues tasks using QueueService with default priority of 5
+- Validates request payload (taskId, agentType, context)
+- Supports all agent types: worker, reviewer, tester
+- Proper error handling and propagation
+- Returns agentId and status to coordinator