fix(container): add /start to filtered commands

Telegram clients send /start when a user first DMs a bot (and when they
tap "Start" on a bot profile). It's a platform handshake, not a
user-intended prompt — forwarding it to the agent wastes a turn and
produces a confused response.

Matches the existing filter pattern for /help, /login, /logout,
/doctor, /config.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

container/agent-runner/src/formatter.ts

@@ -12,7 +12,7 @@ import { TIMEZONE, formatLocalTime } from './timezone.js';
 export type CommandCategory = 'admin' | 'filtered' | 'passthrough' | 'none';
 
 const ADMIN_COMMANDS = new Set(['/remote-control', '/clear', '/compact', '/context', '/cost', '/files']);
-const FILTERED_COMMANDS = new Set(['/help', '/login', '/logout', '/doctor', '/config']);
+const FILTERED_COMMANDS = new Set(['/help', '/login', '/logout', '/doctor', '/config', '/start']);
 
 export interface CommandInfo {
   category: CommandCategory;