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>

docker-compose.yml

@@ -358,6 +358,8 @@ services:
       dockerfile: ./apps/orchestrator/Dockerfile
     container_name: mosaic-orchestrator
     restart: unless-stopped
+    # Run as non-root user (node:node, UID 1000)
+    user: "1000:1000"
     environment:
       NODE_ENV: production
       # Orchestrator Configuration
@@ -377,7 +379,7 @@ services:
     ports:
       - "3002:3001"
     volumes:
-      - /var/run/docker.sock:/var/run/docker.sock
+      - /var/run/docker.sock:/var/run/docker.sock:ro
       - orchestrator_workspace:/workspace
     depends_on:
       valkey:
@@ -392,9 +394,22 @@ services:
       start_period: 40s
     networks:
       - mosaic-internal
+    # Security hardening
+    security_opt:
+      - no-new-privileges:true
+    cap_drop:
+      - ALL
+    cap_add:
+      - NET_BIND_SERVICE
+    read_only: false  # Cannot be read-only due to workspace writes
+    tmpfs:
+      - /tmp:noexec,nosuid,size=100m
     labels:
       - "com.mosaic.service=orchestrator"
       - "com.mosaic.description=Mosaic Agent Orchestrator"
+      - "com.mosaic.security=hardened"
+      - "com.mosaic.security.non-root=true"
+      - "com.mosaic.security.capabilities=minimal"
 
   # ======================
   # Mosaic Web