1. Updated UpdateStripeSettingsRequest - Added publishable_key field
2. Updated update_stripe_settings endpoint - Now validates and stores:
- stripe_publishable_key (not encrypted - it's public)
- stripe_secret_key (encrypted)
- stripe_webhook_secret (encrypted)
- Also validates that publishable and secret keys are from the same environment (both test or both live)
3. Added new public endpoint GET /api/config/stripe - Returns the publishable key to the frontend (no auth required since it's meant to be public)
4. Updated get_stripe_status endpoint - Now includes publishable_key_prefix and publishable_key_set in the response