Fixes #5210: Add warning when deleting modes with associated rules folders

[roomote]

• Enhanced deleteCustomMode confirmation dialog to warn users when .roo/rules-{mode} folder exists
• Added new translation key 'delete_custom_mode_with_rules' for enhanced warning message
• Modified webview message handler to check for rules folder existence before showing confirmation
• Added comprehensive tests covering all scenarios: enhanced warnings, standard warnings, error handling
• Preserves existing behavior for modes without rules folders
• Handles edge cases gracefully (no workspace, file check failures, mode not found)

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Important

Enhance deleteCustomMode to warn users about associated rules folders, with comprehensive tests and edge case handling.

• Behavior:
  • deleteCustomMode now warns if .roo/rules-{mode} folder exists, using new translation key delete_custom_mode_with_rules.
  • Preserves existing behavior for modes without rules folders.
  • Handles edge cases: no workspace, file check failures, mode not found.
• Webview:
  • Modified webviewMessageHandler to check for rules folder before showing confirmation.
• Tests:
  • Added tests in webviewMessageHandler.spec.ts for enhanced warnings, standard warnings, and error handling.

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[delve-auditor]

✅ No security or compliance issues detected. Reviewed everything up to 3b3da61.

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• 🔎 Scanned files: 3 changed file(s)

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