Add React.memo to ThreadListItemComponent to prevent unnecessary re-renders

[MODSetter]

Description

ThreadListItemComponent in thread-list.tsx renders inside a .map() for every chat thread. When the parent re-renders (e.g., switching active thread, toggling archive filter), all thread rows re-render even if their individual props haven't changed. Wrapping the component in React.memo lets React skip re-rendering rows whose props are referentially equal.

Vercel React Best Practices Rule: rerender-memo (5.5)

File to change

• surfsense_web/components/assistant-ui/thread-list.tsx

What to do

1. Add memo to the React import:

import { memo } from "react";

2. Convert ThreadListItemComponent (lines 218-275) from a plain function to a memoized component:

// Before
function ThreadListItemComponent({
  thread, isActive, isArchived, onClick, onArchive, onUnarchive, onDelete,
}: ThreadListItemComponentProps) {
  return ( ... );
}

// After
const ThreadListItemComponent = memo(function ThreadListItemComponent({
  thread, isActive, isArchived, onClick, onArchive, onUnarchive, onDelete,
}: ThreadListItemComponentProps) {
  return ( ... );
});

No other changes needed to the component internals.

Note: For memo to be fully effective, the callbacks passed to each row should also be stable. Currently (lines 195-198), inline arrow functions create new references each render. That's a potential follow-up, but even without it, memo helps when thread and isActive are unchanged (the most common case).

Acceptance criteria

• ThreadListItemComponent is wrapped in React.memo
• Thread list still works: clicking, archiving, unarchiving, deleting all function correctly
• In React DevTools Profiler, unchanged thread rows show as "Did not render" when another row is clicked