feat(chat): polish thread header, emoji picker, and pane gutter

Tier A + B chat-tab visual pass:
- Widen the list<->thread gutter (1px -> 10px) for breathing room.
- Redesign the thread header: avatar + name on the left with a
  right-aligned frameless icon toolbar (add-contact/export/mute/hide,
  each with a tooltip); the name is clipped to the toolbar's left edge
  so a long contact label can't overrun the icons.
- Replace the "Copy Full Address" button with a click-to-copy shortened
  address (copies the full z-addr), preceded by a key-verify lock whose
  tooltip shows a comparable identity-key fingerprint.
- Show a "Waiting for reply" chip in the header when the peer's identity
  key isn't known yet.
- Emoji picker: frameless grid with tight cells (glyphs fill the cell)
  and leftover width spread into the column gaps so it stays edge-to-edge.
- Larger 30px composer emoji toggle that lights up while the picker is
  open; footer height + byte-counter centering adjusted to match.

New i18n keys (chat_copy_address_tip / chat_verify_key / chat_awaiting_key)
added additively to all 8 languages; CJK subset font rebuilt for the new
zh glyph.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

res/lang/ja.json

@@ -136,9 +136,11 @@
     "characters": "文字",
     "chat": "チャット",
     "chat_add_contact": "連絡先に追加",
+    "chat_awaiting_key": "返信待ち",
     "chat_cancel": "キャンセル",
     "chat_contact_added": "連絡先を追加しました — 連絡先で名前を変更できます",
     "chat_contact_request": "連絡リクエスト",
+    "chat_copy_address_tip": "クリックしてアドレスをコピー",
     "chat_emoji_search": "絵文字を検索",
     "chat_empty_hint": "まだ会話はありません。受信したメッセージはここに表示されます。",
     "chat_empty_start": "「新しい会話」から始めましょう。",
@@ -181,6 +183,7 @@
     "chat_toast_waiting_reply": "メッセージを送るには、この相手からの返信を待つ必要があります。",
     "chat_unhide": "再表示",
     "chat_unmute": "ミュート解除",
+    "chat_verify_key": "識別鍵 — 照合して確認",
     "chat_waiting_reply": "この相手からの返信を待っています — 返信があればメッセージを送れます。",
     "chat_you": "自分",
     "choose_icon": "アイコンを選択",