feat: phone login, position badge, logout in profile, global search, admin chats

- Login: by phone number instead of username
- Position field: shown as badge next to name in members list, search, admin panel
- Logout: moved from sidebar to profile modal settings
- Sidebar search: global — shows matching users with one-click private chat
- Admin panel: new Чаты tab showing all chats with delete, position/phone in user form
- Backend: /api/admin/chats endpoint, position column migration, phone login support

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/types.ts

@@ -6,6 +6,7 @@ export interface User {
   avatar?: string | null;
   bio?: string;
   phone?: string;
+  position?: string | null;
   isAdmin: boolean;
   lastSeen?: string;
   online?: boolean;
@@ -17,6 +18,7 @@ export interface ChatMember {
   displayName: string;
   avatarColor: string;
   avatar?: string | null;
+  position?: string | null;
   role: 'owner' | 'admin' | 'member';
   online: boolean;
   lastSeen: string;