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/api/chats.ts

@@ -35,6 +35,21 @@ export async function sendMessage(chatId: number, text: string, type: MessageTyp
   return data;
 }
 
+export async function sendMessageWithClientId(
+  chatId: number,
+  text: string,
+  type: MessageType,
+  clientMessageId: string
+): Promise<Message> {
+  const { data } = await http.post<Message>("/messages", {
+    chat_id: chatId,
+    text,
+    type,
+    client_message_id: clientMessageId
+  });
+  return data;
+}
+
 export interface UploadUrlResponse {
   upload_url: string;
   file_url: string;
@@ -77,3 +92,15 @@ export async function attachFile(messageId: number, fileUrl: string, fileType: s
     file_size: fileSize
   });
 }
+
+export async function updateMessageStatus(
+  chatId: number,
+  messageId: number,
+  status: "message_delivered" | "message_read"
+): Promise<void> {
+  await http.post("/messages/status", {
+    chat_id: chatId,
+    message_id: messageId,
+    status
+  });
+}