feat(cron): make cron tools opt-in via experimental settings

Change cron/loop tools from opt-out to opt-in. Cron tools are now
disabled by default and can be enabled via:
- settings.json: { "experimental": { "cron": true } }
- Environment variable: QWEN_CODE_ENABLE_CRON=1

This ensures experimental features are explicitly enabled by users
who want to try them.

Co-authored-by: Qwen-Coder <qwen-coder@alibabacloud.com>

packages/cli/src/config/config.ts

@@ -1089,6 +1089,7 @@ export async function loadCliConfig(
     maxSessionTurns:
       argv.maxSessionTurns ?? settings.model?.maxSessionTurns ?? -1,
     experimentalZedIntegration: argv.acp || argv.experimentalAcp || false,
+    cronEnabled: settings.experimental?.cron ?? false,
     listExtensions: argv.listExtensions || false,
     overrideExtensions: overrideExtensions || argv.extensions,
     noBrowser: !!process.env['NO_BROWSER'],