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>

packages/cli/src/cli.ts

@@ -0,0 +1,28 @@
+#!/usr/bin/env node
+
+import { Command } from 'commander';
+
+const program = new Command();
+
+program.name('mosaic').description('Mosaic Stack CLI').version('0.0.0');
+
+program
+  .command('tui')
+  .description('Launch interactive TUI connected to the gateway')
+  .option('-g, --gateway <url>', 'Gateway URL', 'http://localhost:4000')
+  .option('-c, --conversation <id>', 'Resume a conversation by ID')
+  .action(async (opts: { gateway: string; conversation?: string }) => {
+    // Dynamic import to avoid loading React/Ink for other commands
+    const { render } = await import('ink');
+    const React = await import('react');
+    const { TuiApp } = await import('./tui/app.js');
+
+    render(
+      React.createElement(TuiApp, {
+        gatewayUrl: opts.gateway,
+        conversationId: opts.conversation,
+      }),
+    );
+  });
+
+program.parse();