feat(history): badge chat transactions + add a Chat filter

Transactions that carried a chat message (sent or received, messages + contact
requests) now show a "Message" badge in the History tab, and a new "Chat" option
in the type-filter combo shows only those transactions.

Detection reuses what the chat store already tracks: ChatStore gains an inline
chatTxids() returning the set of on-chain txids that carried a chat message; the
tab builds it once per frame (cheap — O(chat messages)) and tests txid membership
for the badge and the filter. Empty when chat is disabled or the wallet has no
chat identity. Both variants populate the chat store before this tab renders, so
the same code serves full-node and lite with no separate handling.

The "Message" badge reuses the stacked top-pill slot (chat txs are send/receive,
not the autoshield "shield" type, so it and the "Shielded" badge are mutually
exclusive; chat takes precedence) in a distinct Secondary() colour. Guards the
summary-card accent idx_map so the new filter value (4) can't index it OOB.

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

res/lang/ja.json

@@ -167,6 +167,7 @@
     "chat_export_done": "会話をエクスポートしました",
     "chat_export_failed": "エクスポートファイルを書き込めませんでした。",
     "chat_export_warn": "復号したメッセージを平文で保存します。ファイルは安全に保管してください。",
+    "chat_filter": "チャット",
     "chat_hidden_toast": "会話を非表示にしました — 新しいメッセージが届くと再表示されます",
     "chat_hide": "非表示",
     "chat_hide_hidden": "非表示を隠す",
@@ -1526,6 +1527,7 @@
     "tt_website": "DragonX ウェブサイトを開く",
     "tt_window_opacity": "背景の不透明度（低い = デスクトップがウィンドウ越しに見える）",
     "tt_wizard": "初期セットアップウィザードを再実行\\nデーモンは再起動されます",
+    "tx_chat_badge": "メッセージ",
     "tx_confirmations": "%d 確認",
     "tx_details_title": "取引の詳細",
     "tx_from_address": "送信元アドレス：",