feat: add multi-channel subscription blocking UI and admin management

- 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

src/locales/en.json

@@ -861,7 +861,8 @@
       "updates": "Updates",
       "pinnedMessages": "Pinned Messages",
       "partners": "Partners",
-      "withdrawals": "Withdrawals"
+      "withdrawals": "Withdrawals",
+      "channelSubscriptions": "Required Channels"
     },
     "panel": {
       "title": "Admin Panel",
@@ -888,7 +889,8 @@
       "updatesDesc": "Bot & cabinet versions",
       "pinnedMessagesDesc": "Manage pinned messages for users",
       "partnersDesc": "Manage partner applications and commissions",
-      "withdrawalsDesc": "Review and process withdrawal requests"
+      "withdrawalsDesc": "Review and process withdrawal requests",
+      "channelSubscriptionsDesc": "Manage required channel subscriptions"
     },
     "trafficUsage": {
       "title": "Traffic Usage",
@@ -1297,6 +1299,28 @@
       "editMessage": "Edit",
       "cantDeleteActive": "Cannot delete active message"
     },
+    "channelSubscriptions": {
+      "title": "Required Channels",
+      "subtitle": "Users must subscribe to these channels",
+      "addChannel": "Add Channel",
+      "empty": "No channels configured",
+      "enabled": "Enabled",
+      "disabled": "Disabled",
+      "enable": "Enable",
+      "disable": "Disable",
+      "delete": "Delete",
+      "deleteConfirm": "Delete this channel?",
+      "sortOrder": "Order",
+      "form": {
+        "title": "Display Name",
+        "channelId": "Channel ID",
+        "channelIdHint": "@username or -100XXXXXXXXXX",
+        "channelLink": "Channel Link",
+        "channelLinkHint": "https://t.me/channel",
+        "submit": "Add",
+        "cancel": "Cancel"
+      }
+    },
     "settings": {
       "title": "System Settings",
       "allCategories": "All categories",
@@ -3144,7 +3168,9 @@
       "waitSeconds": "Wait {{seconds}} sec.",
       "hint": "Click check button after subscribing",
       "notSubscribed": "You haven't subscribed to the channel yet",
-      "checkError": "Check failed. Please try again later."
+      "checkError": "Check failed. Please try again later.",
+      "subscribed": "Subscribed",
+      "channelsRequired": "Subscribe to all channels below to continue"
     },
     "blacklisted": {
       "title": "Access Denied",