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/components/MessageInput.tsx

@@ -77,20 +77,29 @@ export default function MessageInput({ chatId, replyTo, editMsg, onCancelReply,
     if (textareaRef.current) textareaRef.current.style.height = 'auto';
     wsClient.send('typing', { chatId, typing: false });
 
-    if (editMsg) {
-      wsClient.send('edit_message', { messageId: editMsg.id, content });
-      onEditDone({ ...editMsg, content, isEdited: true });
-    } else {
-      wsClient.send('send_message', {
-        chatId,
-        content,
-        type: 'text',
-        replyToId: replyTo?.id || null,
-      });
-      onCancelReply();
+    try {
+      if (editMsg) {
+        wsClient.send('edit_message', { messageId: editMsg.id, content });
+        onEditDone({ ...editMsg, content, isEdited: true });
+      } else {
+        const sent = wsClient.trySend('send_message', {
+          chatId, content, type: 'text', replyToId: replyTo?.id || null,
+        });
+        if (!sent) {
+          // WS not available — use HTTP fallback
+          const { data } = await api.post(`/api/messages/chat/${chatId}`, {
+            content, type: 'text', replyToId: replyTo?.id || null,
+          });
+          addMessage(data);
+        }
+        onCancelReply();
+      }
+    } catch {
+      // restore text so user doesn't lose it
+      setText(content);
+    } finally {
+      setSending(false);
     }
-
-    setSending(false);
   }
 
   async function handleFile(e: React.ChangeEvent<HTMLInputElement>) {