feat: add Docker support and inbound webhooks (Tier 2)

- Dockerfile: multi-stage build (node:22-alpine), better-sqlite3 native deps handled
- .dockerignore + docker-compose.yml for deployment
- FLYNN_DATA_DIR env var support in daemon, CLI, and TUI
- WebhookHandler: ChannelAdapter for HTTP POST /webhooks/:name
- Per-webhook HMAC auth, template rendering ({{body}}, {{json.field}})
- Config schema: automation.webhooks array with name/secret/message/output
- Gateway routes webhook requests before static files (bypasses gateway auth)
- 23 new tests for webhook functionality, 874 total tests passing

src/cli/tui.ts

@@ -49,7 +49,7 @@ export function registerTuiCommand(program: Command): void {
       const { HookEngine } = await import('../hooks/index.js');
       const { createModelRouter } = await import('../daemon/index.js');
 
-      const dataDir = resolve(homedir(), '.local/share/flynn');
+      const dataDir = process.env.FLYNN_DATA_DIR ?? resolve(homedir(), '.local/share/flynn');
       mkdirSync(dataDir, { recursive: true });
 
       const sessionStore = new SessionStore(resolve(dataDir, 'sessions.db'));