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/components/MessageComposer.tsx

@@ -1,5 +1,5 @@
 import { useEffect, useRef, useState } from "react";
-import { attachFile, requestUploadUrl, sendMessage, uploadToPresignedUrl } from "../api/chats";
+import { attachFile, requestUploadUrl, sendMessageWithClientId, uploadToPresignedUrl } from "../api/chats";
 import { useAuthStore } from "../store/authStore";
 import { useChatStore } from "../store/chatStore";
 import { buildWsUrl } from "../utils/ws";
@@ -28,6 +28,13 @@ export function MessageComposer() {
     };
   }, [previewUrl]);
 
+  function makeClientMessageId(): string {
+    if (typeof crypto !== "undefined" && "randomUUID" in crypto) {
+      return crypto.randomUUID();
+    }
+    return `msg-${Date.now()}-${Math.random().toString(16).slice(2)}`;
+  }
+
   function getWs(): WebSocket | null {
     if (!accessToken || !activeChatId) {
       return null;
@@ -44,7 +51,7 @@ export function MessageComposer() {
     if (!activeChatId || !text.trim()) {
       return;
     }
-    const message = await sendMessage(activeChatId, text.trim(), "text");
+    const message = await sendMessageWithClientId(activeChatId, text.trim(), "text", makeClientMessageId());
     prependMessage(activeChatId, message);
     setText("");
     const ws = getWs();
@@ -61,7 +68,7 @@ export function MessageComposer() {
     try {
       const upload = await requestUploadUrl(file);
       await uploadToPresignedUrl(upload.upload_url, upload.required_headers, file, setUploadProgress);
-      const message = await sendMessage(activeChatId, upload.file_url, messageType);
+      const message = await sendMessageWithClientId(activeChatId, upload.file_url, messageType, makeClientMessageId());
       await attachFile(message.id, upload.file_url, file.type || "application/octet-stream", file.size);
       prependMessage(activeChatId, message);
     } catch {