feat: communication spine — gateway, TUI, Discord

Gateway:
- Agent service wrapping Pi SDK createAgentSession (in-process)
- Chat WebSocket gateway (Socket.IO) streaming agent events
- Chat REST controller for synchronous requests
- NestJS module structure: AgentModule (global), ChatModule

CLI:
- Ink-based TUI client connecting to gateway via WebSocket
- Commander-based CLI with `mosaic tui` command
- Streaming message display with React components

Discord:
- Discord.js bot with mention-based activation + DM support
- Routes messages through gateway WebSocket
- Chunked response delivery (2000-char Discord limit)
- Single-guild binding for v0.1.0

Architecture: All channels → Gateway WebSocket → Pi SDK → LLM

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/gateway/package.json

@@ -5,7 +5,7 @@
   "main": "dist/main.js",
   "scripts": {
     "build": "tsc",
-    "dev": "tsc --watch",
+    "dev": "tsx watch src/main.ts",
     "lint": "eslint src",
     "typecheck": "tsc --noEmit",
     "test": "vitest run"
@@ -14,12 +14,19 @@
     "@nestjs/common": "^11.0.0",
     "@nestjs/core": "^11.0.0",
     "@nestjs/platform-fastify": "^11.0.0",
+    "@nestjs/platform-socket.io": "^11.0.0",
+    "@nestjs/websockets": "^11.0.0",
+    "@mariozechner/pi-coding-agent": "~0.57.1",
     "fastify": "^5.0.0",
     "reflect-metadata": "^0.2.0",
-    "rxjs": "^7.8.0"
+    "rxjs": "^7.8.0",
+    "socket.io": "^4.8.0",
+    "uuid": "^11.0.0"
   },
   "devDependencies": {
     "@types/node": "^22.0.0",
+    "@types/uuid": "^10.0.0",
+    "tsx": "^4.0.0",
     "typescript": "^5.8.0",
     "vitest": "^2.0.0"
   }