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-111-worktrees.md

@@ -47,6 +47,7 @@ git worktree prune
 Worktrees will be named: `agent-{agentId}-{taskId}`
 
 Example:
+
 - `agent-abc123-task-456`
 - `agent-def789-task-789`
 
@@ -87,17 +88,17 @@ class WorktreeManagerService {
     repoPath: string,
     agentId: string,
     taskId: string,
-    baseBranch: string = 'develop'
-  ): Promise<WorktreeInfo>
+    baseBranch: string = "develop"
+  ): Promise<WorktreeInfo>;
 
   // Remove worktree
-  async removeWorktree(worktreePath: string): Promise<void>
+  async removeWorktree(worktreePath: string): Promise<void>;
 
   // List all worktrees for a repo
-  async listWorktrees(repoPath: string): Promise<WorktreeInfo[]>
+  async listWorktrees(repoPath: string): Promise<WorktreeInfo[]>;
 
   // Cleanup worktree on agent completion
-  async cleanupWorktree(agentId: string, taskId: string): Promise<void>
+  async cleanupWorktree(agentId: string, taskId: string): Promise<void>;
 }
 ```