Closes #161

Account Deletion Confirmation Flow

Summary

Adds a safeguarded account deletion flow in dashboard settings. Users must acknowledge the consequences and confirm their identity with their current password before deletion.

Changes

• Added a Delete Account button in the Settings danger zone.
• Added a three-step deletion modal:
  1. Consequences warning and acknowledgment checkbox
  2. Current password confirmation
  3. Success message with a five-second redirect to the homepage
• Added account deletion API support through usersApi.
• Added account deletion handling to useAuthStore.
• Clears authentication state after successful deletion.
• Revokes enrolled course access through the account deletion request.

Acceptance Criteria

• Three-step flow renders in the correct order.
• Users cannot continue without checking “I understand”.
• Password confirmation is required before deletion.
• Successful deletion redirects to the homepage after five seconds.
• Authentication state is cleared after deletion.

Testing

• TypeScript/editor diagnostics pass for all changed files.
• Automated tests and production build could not be run because dependencies were unavailable and npm install stalled.