Add a "Recently used" section to the emoji picker (#35)

Shows up to 8 most-recently-picked emoji, pinned above the regular
categories, whenever the picker isn't in search mode -- shared by both
the composer's insert-emoji button and message reactions, since both
go through the same EmojiPicker component. Stored in localStorage
(frontend/src/lib/recentEmoji.ts), per-browser rather than synced
across devices, matching this app's existing local-only preferences
(e.g. the resizable-panel widths).

Verified in-browser: no section when empty, a pick is recorded and
shows up on reopen, order is most-recent-first, re-picking an already-
recent emoji moves it to the front without duplicating, and the list
caps at 8 by dropping the oldest entry.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

frontend/src/components/EmojiPicker.tsx

@@ -2,6 +2,7 @@ import { useMemo, useState } from 'react'
 import { useEscapeKey } from '../hooks/useEscapeKey'
 import { ALL_EMOJI, EMOJI_CATEGORIES } from '../lib/emoji'
 import { EMOJI_NAMES } from '../lib/emojiNames'
+import { getRecentEmoji, recordEmojiUsed } from '../lib/recentEmoji'
 import './EmojiPicker.css'
 
 interface EmojiPickerProps {
@@ -39,6 +40,16 @@ export function EmojiPicker({ onPick, onClose, placement = 'below', align = 'lef
   const [query, setQuery] = useState('')
   const searchResults = useMemo(() => searchEmoji(query), [query])
   const searching = query.trim().length > 0
+  // A snapshot taken once when the picker opens, not live-updating as picks
+  // happen within this same session -- picking an emoji always closes the
+  // picker (see Composer.tsx/MessageList.tsx), so there's never a second
+  // pick in the same open session to show an updated list to.
+  const [recent] = useState(getRecentEmoji)
+
+  function pick(emoji: string) {
+    recordEmojiUsed(emoji)
+    onPick(emoji)
+  }
 
   return (
     <>
@@ -65,7 +76,7 @@ export function EmojiPicker({ onPick, onClose, placement = 'below', align = 'lef
                   role="menuitem"
                   className="emoji-picker-item"
                   title={EMOJI_NAMES[emoji]?.name}
-                  onClick={() => onPick(emoji)}
+                  onClick={() => pick(emoji)}
                 >
                   {emoji}
                 </button>
@@ -75,7 +86,27 @@ export function EmojiPicker({ onPick, onClose, placement = 'below', align = 'lef
             <div className="emoji-picker-no-results">No emoji found</div>
           )
         ) : (
-          EMOJI_CATEGORIES.map((category) => (
+          <>
+            {recent.length > 0 && (
+              <div className="emoji-picker-category">
+                <div className="emoji-picker-category-label">Recently used</div>
+                <div className="emoji-picker-grid">
+                  {recent.map((emoji) => (
+                    <button
+                      key={emoji}
+                      type="button"
+                      role="menuitem"
+                      className="emoji-picker-item"
+                      title={EMOJI_NAMES[emoji]?.name}
+                      onClick={() => pick(emoji)}
+                    >
+                      {emoji}
+                    </button>
+                  ))}
+                </div>
+              </div>
+            )}
+            {EMOJI_CATEGORIES.map((category) => (
               <div key={category.label} className="emoji-picker-category">
                 <div className="emoji-picker-category-label">{category.label}</div>
                 <div className="emoji-picker-grid">
@@ -86,14 +117,15 @@ export function EmojiPicker({ onPick, onClose, placement = 'below', align = 'lef
                       role="menuitem"
                       className="emoji-picker-item"
                       title={EMOJI_NAMES[emoji]?.name}
-                    onClick={() => onPick(emoji)}
+                      onClick={() => pick(emoji)}
                     >
                       {emoji}
                     </button>
                   ))}
                 </div>
               </div>
-          ))
+            ))}
+          </>
         )}
       </div>
     </>

frontend/src/lib/recentEmoji.ts

@@ -0,0 +1,26 @@
+const KEY = 'recent-emoji'
+const MAX_RECENT = 8
+
+export function getRecentEmoji(): string[] {
+  try {
+    const raw = localStorage.getItem(KEY)
+    if (!raw) return []
+    const parsed = JSON.parse(raw)
+    return Array.isArray(parsed) ? parsed.filter((e) => typeof e === 'string') : []
+  } catch {
+    return []
+  }
+}
+
+// Most-recently-used first, deduped, capped -- a picked emoji that's
+// already in the list moves to the front rather than appearing twice.
+export function recordEmojiUsed(emoji: string): void {
+  try {
+    const current = getRecentEmoji().filter((e) => e !== emoji)
+    const next = [emoji, ...current].slice(0, MAX_RECENT)
+    localStorage.setItem(KEY, JSON.stringify(next))
+  } catch {
+    // storage unavailable (private browsing, quota) -- recent emoji just
+    // won't persist this session, not fatal.
+  }
+}