feat(M6): Set up orchestrator service foundation

Add NestJS-based orchestrator service structure for M6-AgentOrchestration.

Changes:
- Migrate from Express to NestJS architecture
- Add health check endpoint module
- Add placeholder modules: coordinator, git, killswitch, monitor, queue, spawner, valkey
- Update configuration for NestJS
- Update lockfile for new dependencies

This is foundational work for M6-AgentOrchestration milestone.

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

apps/orchestrator/README.md

@@ -1,10 +1,11 @@
 # Mosaic Orchestrator
 
-Agent orchestration service for Mosaic Stack.
+Agent orchestration service for Mosaic Stack built with NestJS.
 
 ## Overview
 
 The Orchestrator is the execution plane of Mosaic Stack, responsible for:
+
 - Spawning and managing Claude agents
 - Task queue management (Valkey-backed)
 - Agent health monitoring and recovery
@@ -25,19 +26,36 @@ Monitored via `apps/web/` (Agent Dashboard).
 # Install dependencies (from monorepo root)
 pnpm install
 
-# Run in dev mode
+# Run in dev mode (watch mode)
 pnpm --filter @mosaic/orchestrator dev
 
 # Build
 pnpm --filter @mosaic/orchestrator build
 
+# Start production
+pnpm --filter @mosaic/orchestrator start:prod
+
 # Test
 pnpm --filter @mosaic/orchestrator test
+
+# Generate module (NestJS CLI)
+cd apps/orchestrator
+nest generate module <name>
+nest generate controller <name>
+nest generate service <name>
 ```
 
+## NestJS Architecture
+
+- **Modules:** Feature-based organization (spawner, queue, monitor, etc.)
+- **Controllers:** HTTP endpoints (health, agents, tasks)
+- **Services:** Business logic
+- **Providers:** Dependency injection
+
 ## Configuration
 
-See `.env.example` for required environment variables.
+Environment variables loaded via @nestjs/config.
+See `.env.example` for required vars.
 
 ## Documentation