fix: chat — VARCHAR(10) overflow for notifications type, skeleton loading

- Migration 072: widen type column to VARCHAR(20), add partial unique index for general rooms
- Backend: replace brittle ON CONFLICT with explicit SELECT-then-INSERT ensureRoom helper
- Frontend: show room skeletons (Общий чат + Уведомления) during load instead of spinner,
  hide '0 чатов' subtitle when list is empty

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

src/components/chat/ChatWidget.tsx

@@ -322,7 +322,7 @@ export function ChatWidget() {
                 {view === 'search' && 'Поиск'}
                 {view === 'settings' && 'Настройки чата'}
               </p>
-              {view === 'rooms' && (
+              {view === 'rooms' && visibleRooms.length > 0 && (
                 <p className="text-xs text-white/70">{visibleRooms.length} чатов</p>
               )}
               {view === 'messages' && activeRoom?.type === 'notifications' && (
@@ -348,10 +348,12 @@ export function ChatWidget() {
           {/* ── Rooms list ── */}
           {view === 'rooms' && (
             <div className="flex-1 overflow-y-auto">
-              {loadingRooms ? (
-                <div className="flex items-center justify-center h-32">
-                  <Loader2 size={20} className="animate-spin text-slate-400" />
-                </div>
+              {loadingRooms && visibleRooms.length === 0 ? (
+                // Skeleton placeholders while loading
+                <>
+                  <RoomSkeleton icon={<Users size={16} className="text-brand-400" />} bg="bg-brand-100 dark:bg-brand-900/30" label="Общий чат" />
+                  {settings.notifVisible && <RoomSkeleton icon={<Bell size={16} className="text-amber-500" />} bg="bg-amber-100 dark:bg-amber-900/30" label="Уведомления" />}
+                </>
               ) : visibleRooms.length === 0 ? (
                 <div className="text-center py-10 text-sm text-slate-400 px-4">
                   Нет чатов. Нажмите <PenSquare size={13} className="inline" /> чтобы начать.
@@ -681,3 +683,17 @@ function ToggleRow({ icon, label, checked, onChange }: {
     </div>
   )
 }
+
+function RoomSkeleton({ icon, bg, label }: { icon: React.ReactNode; bg: string; label: string }) {
+  return (
+    <div className="flex items-center gap-3 px-4 py-3 border-b border-slate-100 dark:border-slate-700/50 animate-pulse">
+      <div className={cn('w-9 h-9 rounded-full flex items-center justify-center shrink-0', bg)}>
+        {icon}
+      </div>
+      <div className="flex-1 min-w-0">
+        <p className="text-sm font-medium text-slate-600 dark:text-slate-300">{label}</p>
+        <div className="h-3 w-24 bg-slate-200 dark:bg-slate-600 rounded mt-1" />
+      </div>
+    </div>
+  )
+}