feat: add admin pinned messages section

- API client with full CRUD, broadcast, activate/deactivate, unpin endpoints
- List page with active/inactive badges, action buttons, pagination
- Create/edit form with content editor, media upload, display settings toggles
- Routes and navigation in admin marketing group
- i18n translations for ru, en, fa, zh

src/locales/en.json

@@ -768,7 +768,8 @@
       "promocodes": "Promo Codes",
       "promoGroups": "Discount Groups",
       "trafficUsage": "Traffic Usage",
-      "updates": "Updates"
+      "updates": "Updates",
+      "pinnedMessages": "Pinned Messages"
     },
     "panel": {
       "title": "Admin Panel",
@@ -792,7 +793,8 @@
       "promocodesDesc": "Manage promo codes",
       "promoGroupsDesc": "Discount groups for users",
       "trafficUsageDesc": "Per-user traffic by nodes",
-      "updatesDesc": "Bot & cabinet versions"
+      "updatesDesc": "Bot & cabinet versions",
+      "pinnedMessagesDesc": "Manage pinned messages for users"
     },
     "trafficUsage": {
       "title": "Traffic Usage",
@@ -1157,6 +1159,48 @@
       "bothCreated": "Broadcasts created",
       "atLeastOneChannel": "Select at least one channel"
     },
+    "pinnedMessages": {
+      "title": "Pinned Messages",
+      "subtitle": "Manage pinned messages for users",
+      "create": "Create",
+      "empty": "No pinned messages",
+      "content": "Message text",
+      "contentPlaceholder": "Enter pinned message text...",
+      "noContent": "No text",
+      "media": "Media file",
+      "addMedia": "Add media",
+      "uploading": "Uploading...",
+      "settings": "Settings",
+      "sendBeforeMenu": "Send before menu",
+      "sendOnEveryStart": "Send on every start",
+      "broadcast": "Broadcast",
+      "broadcastOnCreate": "Broadcast on create",
+      "broadcastConfirm": "Broadcast pinned message to all active users?",
+      "broadcastToAll": "Broadcast to all",
+      "activate": "Activate",
+      "deactivate": "Deactivate",
+      "unpin": "Unpin",
+      "unpinAll": "Unpin for everyone",
+      "unpinConfirm": "Unpin message for all users?",
+      "delete": "Delete",
+      "deleteConfirm": "Delete this pinned message?",
+      "active": "Active",
+      "inactive": "Inactive",
+      "prev": "Previous",
+      "next": "Next",
+      "createSuccess": "Pinned message created",
+      "updateSuccess": "Message updated",
+      "deleteSuccess": "Message deleted",
+      "activateSuccess": "Message activated",
+      "deactivateSuccess": "Message deactivated",
+      "broadcastSuccess": "Broadcast completed",
+      "unpinSuccess": "Messages unpinned",
+      "sentCount": "Sent",
+      "failedCount": "Failed",
+      "unpinnedCount": "Unpinned",
+      "editMessage": "Edit",
+      "cantDeleteActive": "Cannot delete active message"
+    },
     "settings": {
       "title": "System Settings",
       "allCategories": "All categories",