- Add global settings section (CHANNEL_IS_REQUIRED_SUB, trial/paid toggles)
at top of AdminChannelSubscriptions page
- Add per-channel disable_trial_on_leave and disable_paid_on_leave toggles
in each channel card with inline Toggle controls
- Update RequiredChannel type and API request interfaces with new fields
- Add translations for globalSettings and perChannel in en/ru/fa/zh locales
- Channel subscription blocking screen with per-channel status display
- Safe URL handling with protocol validation (no open redirect)
- Race-condition-safe subscription check with useRef guard
- Admin channel management page with create, toggle, delete
- Error handlers on all admin mutations with haptic feedback
- Proper type guard for channel subscription error detection
- Accessibility: aria-labels on icon-only buttons
- Localization: en, ru, zh, fa translations
