Studio CLI: Add support for xdebug beta flag

[bcotrim]

Related issues

• Fixes STU-1165

Proposed Changes

• Add studio site set-xdebug <enable> command to enable/disable xdebug for a site
• Pass xdebug configuration to the Playground CLI when starting sites
• Respect both the beta feature flag (xdebugSupport) and per-site setting (enableXdebug)
• Add helper function isXdebugBetaEnabled() to check the beta feature flag

Testing Instructions

1. Enable the xdebug beta feature in Studio desktop app (Settings > Beta Features > Xdebug Support)
2. Build the CLI: npm run cli:build
3. Create or use an existing site: node dist/cli/main.js site create --name test-xdebug --path /tmp/xdebug-test
4. Enable xdebug for the site: node dist/cli/main.js site set-xdebug true --path /tmp/xdebug-test
5. Start the site: node dist/cli/main.js site start --path /tmp/xdebug-test
6. Verify xdebug is enabled by checking the site or PM2 logs for "Enabling Xdebug support" message
7. Test disabling: node dist/cli/main.js site set-xdebug false --path /tmp/xdebug-test
8. Restart the site and verify xdebug is no longer enabled

Edge cases to verify:

• Site starts normally without xdebug when beta flag is off
• Site starts normally without xdebug when site setting is off (even if beta flag is on)
• Error message shown when trying to enable xdebug but beta flag is off

Pre-merge Checklist

• Have you checked for TypeScript, React or other console errors?