feat: add message reliability foundation

- implement idempotent message creation via client_message_id

- add persistent delivered/read receipts

- expose /messages/status and wire websocket receipt events

- update web client to send client ids and auto-ack delivered/read

web/src/hooks/useRealtime.ts

@@ -16,6 +16,7 @@ export function useRealtime() {
   const prependMessage = useChatStore((s) => s.prependMessage);
   const loadChats = useChatStore((s) => s.loadChats);
   const chats = useChatStore((s) => s.chats);
+  const activeChatId = useChatStore((s) => s.activeChatId);
   const typingByChat = useRef<Record<number, Set<number>>>({});
 
   const wsUrl = useMemo(() => {
@@ -34,6 +35,12 @@ export function useRealtime() {
         const chatId = Number(event.payload.chat_id);
         const message = event.payload.message as Message;
         prependMessage(chatId, message);
+        if (message.sender_id !== me?.id) {
+          ws.send(JSON.stringify({ event: "message_delivered", payload: { chat_id: chatId, message_id: message.id } }));
+          if (chatId === activeChatId) {
+            ws.send(JSON.stringify({ event: "message_read", payload: { chat_id: chatId, message_id: message.id } }));
+          }
+        }
         if (!chats.some((chat) => chat.id === chatId)) {
           void loadChats();
         }
@@ -59,7 +66,7 @@ export function useRealtime() {
     };
 
     return () => ws.close();
-  }, [wsUrl, prependMessage, loadChats, chats, me?.id]);
+  }, [wsUrl, prependMessage, loadChats, chats, me?.id, activeChatId]);
 
   return null;
 }