fix: message sending fallback + iOS zoom on input + openOrCreatePrivate

- MessageInput: HTTP fallback when WebSocket not OPEN (prevents silent failures)
- WsClient: add trySend() returning bool to detect WS availability
- Backend: POST /api/messages/chat/:chatId endpoint for HTTP message send
- openOrCreatePrivate: use openChat() for consistency after refreshing chat list
- iOS fix: inputs get font-size:16px on mobile to prevent Safari auto-zoom

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

frontend/src/pages/MainLayout.tsx

@@ -90,16 +90,19 @@ export default function MainLayout() {
     try {
       const { data: chatData } = await api.post(`/api/chats/private/${userId}`);
       setSearch('');
-      // Load full chat detail directly by ID — don't rely on list lookup
-      const { data: fullChatData } = await api.get(`/api/chats/${chatData.id}`);
-      // Also refresh the sidebar chat list
-      api.get('/api/chats').then(r => setChats(r.data)).catch(() => {});
-      // Build chat object to open
-      const chatToOpen = { ...fullChatData, id: chatData.id };
-      setActiveChat(chatToOpen);
-      setFullChat(chatToOpen);
-      setMobileChatOpen(true);
-      setShowInfo(false);
+      const { data: allChats } = await api.get('/api/chats');
+      setChats(allChats);
+      const chatFromList = allChats.find((c: any) => c.id === chatData.id);
+      if (chatFromList) {
+        await openChat(chatFromList);
+      } else {
+        // fallback: open by direct API call
+        const { data: fullChatData } = await api.get(`/api/chats/${chatData.id}`);
+        setActiveChat(fullChatData);
+        setFullChat(fullChatData);
+        setMobileChatOpen(true);
+        setShowInfo(false);
+      }
     } catch (e) {
       console.error('openOrCreatePrivate:', e);
     }