feat(stickers): "recently used" row in the sticker picker

The emoji and GIF pickers both have a "Recent" row, but the sticker tab of the
shared EmojiBoard did not — you had to hunt through packs to re-send a sticker.
Add recent stickers, mirroring recentGifs:

- New state/recentStickers.ts (localStorage cinny_recent_stickers_v1, deduped by
  url, capped 16) + pure addRecentSticker with 4 unit tests.
- EmojiBoard: a "Recent" group in stickerGroupItems and a RecentClock sidebar
  icon in StickerSidebar, shown only when recents exist. Entries are rebuilt into
  minimal PackImageReaders (StickerItem needs only url/shortcode/body) so they
  render + re-send like pack stickers.
- Recorded on select in the shared delegated click handler, covering both the
  grouped and search paths.

Blast radius is the sticker tab only (reactions/status use the emoji tab).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/components/emoji-board/EmojiBoard.tsx

@@ -14,7 +14,7 @@ import { Box, config, Icons, Scroll } from 'folds';
 import FocusTrap from 'focus-trap-react';
 import { isKeyHotkey } from 'is-hotkey';
 import { Room } from 'matrix-js-sdk';
-import { atom, PrimitiveAtom, useAtom, useSetAtom } from 'jotai';
+import { atom, PrimitiveAtom, useAtom, useAtomValue, useSetAtom } from 'jotai';
 import { useVirtualizer } from '@tanstack/react-virtual';
 import { EmojiData, IEmoji, emojiGroups, emojis, loadEmojiData } from '../../plugins/emoji';
 import { useEmojiGroupLabels } from './useEmojiGroupLabels';
@@ -29,6 +29,7 @@ import { useAsyncSearch, UseAsyncSearchOptions } from '../../hooks/useAsyncSearc
 import { useDebounce } from '../../hooks/useDebounce';
 import { useThrottle } from '../../hooks/useThrottle';
 import { addRecentEmoji } from '../../plugins/recent-emoji';
+import { addRecentSticker, recentStickersAtom } from '../../state/recentStickers';
 import { useMediaAuthentication } from '../../hooks/useMediaAuthentication';
 import { ImagePack, ImageUsage, PackImageReader } from '../../plugins/custom-emoji';
 import { getEmoticonSearchStr } from '../../plugins/utils';
@@ -102,6 +103,7 @@ const useGroups = (
   const mx = useMatrixClient();
 
   const recentEmojis = useRecentEmoji(mx, 21);
+  const recentStickers = useAtomValue(recentStickersAtom);
   const labels = useEmojiGroupLabels();
   const { emojiGroups: loadedEmojiGroups } = useEmojiData();
 
@@ -143,6 +145,18 @@ const useGroups = (
     const g: StickerGroupItem[] = [];
     if (tab !== EmojiBoardTab.Sticker) return g;
 
+    if (recentStickers.length > 0) {
+      g.push({
+        id: RECENT_GROUP_ID,
+        name: 'Recent',
+        // StickerItem only reads url/shortcode/body, so a minimal PackImageReader
+        // reconstructed from the stored data renders and re-sends correctly.
+        items: recentStickers.map(
+          (s) => new PackImageReader(s.shortcode, s.url, { body: s.body })
+        ),
+      });
+    }
+
     imagePacks.forEach((pack) => {
       let label = pack.meta.name;
       if (!label) label = isUserId(pack.id) ? 'Personal Pack' : mx.getRoom(pack.id)?.name;
@@ -157,7 +171,7 @@ const useGroups = (
     });
 
     return g;
-  }, [mx, imagePacks, tab]);
+  }, [mx, imagePacks, tab, recentStickers]);
 
   return [emojiGroupItems, stickerGroupItems];
 };
@@ -289,6 +303,7 @@ function StickerSidebar({ activeGroupAtom, packs, onScrollToGroup }: StickerSide
   const useAuthentication = useMediaAuthentication();
 
   const [activeGroupId, setActiveGroupId] = useAtom(activeGroupAtom);
+  const recentStickers = useAtomValue(recentStickersAtom);
   const usage = ImageUsage.Sticker;
 
   const packLabels = useMemo(() => {
@@ -308,6 +323,17 @@ function StickerSidebar({ activeGroupAtom, packs, onScrollToGroup }: StickerSide
 
   return (
     <Sidebar>
+      {recentStickers.length > 0 && (
+        <SidebarStack>
+          <GroupIcon
+            active={activeGroupId === RECENT_GROUP_ID}
+            id={RECENT_GROUP_ID}
+            label="Recent"
+            icon={Icons.RecentClock}
+            onClick={handleScrollToGroup}
+          />
+        </SidebarStack>
+      )}
       <SidebarStack>
         {packs.map((pack) => {
           const label = packLabels.get(pack.id);
@@ -435,6 +461,7 @@ export function EmojiBoard({
   );
   const activeGroupIdAtom = useMemo(() => atom<string | undefined>(undefined), []);
   const setActiveGroupId = useSetAtom(activeGroupIdAtom);
+  const setRecentStickers = useSetAtom(recentStickersAtom);
   const imagePacks = useRelevantImagePacks(usage, imagePackRooms);
   const [emojiGroupItems, stickerGroupItems] = useGroups(tab, imagePacks);
   const groups = emojiTab ? emojiGroupItems : stickerGroupItems;
@@ -494,6 +521,13 @@ export function EmojiBoard({
     }
     if (emojiInfo.type === EmojiType.Sticker) {
       onStickerSelect?.(emojiInfo.data, emojiInfo.shortcode, emojiInfo.label);
+      setRecentStickers((prev) =>
+        addRecentSticker(prev, {
+          url: emojiInfo.data,
+          shortcode: emojiInfo.shortcode,
+          body: emojiInfo.label,
+        })
+      );
     }
     if (!evt.altKey && !evt.shiftKey) requestClose();
   };