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/design/architecture-decisions.md

@@ -67,12 +67,14 @@ Mosaic Stack needs to integrate with AI agents (currently ClawdBot, formerly Mol
 ### Consequences
 
 **Positive:**
+
 - Platform independence
 - Multiple integration paths
 - Clear separation of concerns
 - Easier testing (API-level tests)
 
 **Negative:**
+
 - Extra network hop for agent access
 - Need to maintain both API and skill code
 - Slightly more initial work
@@ -80,8 +82,8 @@ Mosaic Stack needs to integrate with AI agents (currently ClawdBot, formerly Mol
 ### Related Issues
 
 - #22: Brain query API endpoint (API-first ✓)
-- #23-26: mosaic-plugin-* → rename to mosaic-skill-* (thin wrappers)
+- #23-26: mosaic-plugin-_ → rename to mosaic-skill-_ (thin wrappers)
 
 ---
 
-*Future ADRs will be added to this document.*
+_Future ADRs will be added to this document._