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>

src/util/i18n.cpp

@@ -260,6 +260,9 @@ void I18n::loadBuiltinEnglish()
         strings_["chat_hidden_toast"] = "Conversation hidden — a new message brings it back";
         strings_["chat_pick_contact"] = "Choose from contacts\xE2\x80\xA6";
         strings_["chat_no_z_contacts"] = "No shielded-address contacts yet";
+        strings_["chat_copy_address_tip"] = "Click to copy address";
+        strings_["chat_verify_key"] = "Identity key \xE2\x80\x94 compare to verify";
+        strings_["chat_awaiting_key"] = "Waiting for reply";
         // Seed-phrase backup (full-node)
         strings_["seed_backup_button"] = "Seed phrase";
         strings_["tt_seed_backup"] = "Show and back up your wallet's 24-word recovery seed phrase";