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 <[email protected]>

apps/orchestrator/eslint.config.js

@@ -0,0 +1,16 @@
+import nestjsConfig from "@mosaic/config/eslint/nestjs";
+
+export default [
+  ...nestjsConfig,
+  {
+    languageOptions: {
+      parserOptions: {
+        project: ["./tsconfig.json"],
+        tsconfigRootDir: import.meta.dirname,
+      },
+    },
+  },
+  {
+    ignores: ["dist/**", "node_modules/**", "**/*.test.ts", "**/*.spec.ts"],
+  },
+];