fix: mention closure, onSettled invalidation, cleanup singleton

- Fix Tiptap mention: pass QueryClient via closure from ContentEditor
  instead of getQueryClient() singleton (resolves @mention empty list)
- Add onSettled invalidation to useUpdateIssue (prevents cache drift
  with staleTime: Infinity + self-event WS filter)
- Add cache shape comment to issueListOptions (select transforms
  ListIssuesResponse → Issue[], but cache stores raw response)
- Memoize sidebar inbox dedup computation
- Remove dead getQueryClient/setQueryClient singleton + window property
- Remove ActorSync component and _members/_agents Zustand mirror
  (superseded by closure approach)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/web/features/editor/content-editor.tsx

@@ -34,6 +34,7 @@ import {
 import { useEditor, EditorContent } from "@tiptap/react";
 import { cn } from "@/lib/utils";
 import type { UploadResult } from "@/shared/hooks/use-file-upload";
+import { useQueryClient } from "@tanstack/react-query";
 import { createEditorExtensions } from "./extensions";
 import { uploadAndInsertFile } from "./extensions/file-upload";
 import { preprocessMarkdown } from "./utils/preprocess";
@@ -94,6 +95,8 @@ const ContentEditor = forwardRef<ContentEditorRef, ContentEditorProps>(
     onBlurRef.current = onBlur;
     onUploadFileRef.current = onUploadFile;
 
+    const queryClient = useQueryClient();
+
     const editor = useEditor({
       immediatelyRender: false,
       editable,
@@ -102,6 +105,7 @@ const ContentEditor = forwardRef<ContentEditorRef, ContentEditorProps>(
       extensions: createEditorExtensions({
         editable,
         placeholder: placeholderText,
+        queryClient,
         onSubmitRef,
         onUploadFileRef,
       }),