feat(citations): add shared citation components and optimize code

## New Features
- Add `CitationLink` shared component for rendering citation hover cards
- Add `CitationsLoadingIndicator` component for showing loading state
- Add `removeAllCitations` utility to strip all citations from content
- Add backend support for removing citations when downloading markdown files
- Add i18n support for citation loading messages (en-US, zh-CN)

## Code Optimizations
- Remove duplicate `ExternalLinkBadge` component, reuse `CitationLink` instead
- Consolidate `remarkPlugins` config in `streamdownPlugins` to avoid duplication
- Remove unused imports: `Citation`, `buildCitationMap`, `extractDomainFromUrl`, etc.
- Remove unused `messages` parameter from `ToolCall` component
- Remove unused `isWriteFile` parameter from `ArtifactFilePreview` component
- Remove unused `useI18n` hook from `MessageContent` component

## Bug Fixes
- Fix `remarkGfm` plugin configuration that prevented table rendering
- Fix React Hooks rule violation: move `useMemo` to component top level
- Replace `||` with `??` for nullish coalescing in clipboard data

## Code Cleanup
- Remove debug console.log/info statements from:
  - `threads/hooks.ts`
  - `notification/hooks.ts`
  - `memory-settings-page.tsx`
- Fix import order in `message-group.tsx`

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/src/core/threads/hooks.ts

@@ -206,12 +206,6 @@ export function useRenameThread() {
       });
     },
     onSuccess(_, { threadId, title }) {
-      queryClient.setQueryData(
-        ["thread", "state", threadId],
-        (oldData: Array<AgentThread>) => {
-          console.info("oldData", oldData);
-        },
-      );
       queryClient.setQueriesData(
         {
           queryKey: ["threads", "search"],