Add configurable trading hours setting

Dropdown on settings page with two options:
- Full CME (5:00 PM – 3:00 PM CT) with 5 min buffer
- Equity Hours (8:30 AM – 3:00 PM CT) with 5 min buffer
Setting is read live each tick, no restart needed.

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

lib/db.ts

@@ -164,6 +164,7 @@ seedSetting.run('max_concurrent_accounts', '5');
 seedSetting.run('tick_interval_seconds', '60');
 seedSetting.run('master_dashboard_url', '');
 seedSetting.run('instance_name', '');
+seedSetting.run('trading_hours', 'full_cme');
 
 export function getSetting(key: string): string | null {
     const row = db.prepare('SELECT value FROM settings WHERE key = ?').get(key) as { value: string } | undefined;