fix: recover chat replies and organize setup navigation [skip ci]

Targeted source-only patch from reviewed local e370485. Adds bounded realtime/catch-up recovery and moves the setup wizard under System. Static checks only; regression tests, full build and runtime verification have not been run. No deployment. Separate hardening-review branch is not merged. Expected tree: 6235478b9a.

web/lib/api/im.ts

@@ -1,3 +1,4 @@
+// Modified for targeted chat realtime recovery; see docs/fixes/chat-realtime-recovery.md.
 import { request } from "@/lib/api/client"
 import { translateCurrentMessage } from "@/i18n/messages"
 import { readSupportChatRuntimeConfig } from "@/lib/sdk/runtime-config"
@@ -472,11 +473,12 @@ export function fetchImConversationDetail(id: number) {
 }
 
 export function fetchImMessages(
-  query?: Record<string, string | number | undefined>
+  query?: Record<string, string | number | undefined>,
+  options?: { signal?: AbortSignal }
 ) {
   return request<PageResult<ImMessage>>(
     `/api/message/list${toQueryString(query)}`,
-    createRequestOptions()
+    createRequestOptions({ signal: options?.signal })
   )
 }