feat(ui): migrate Explorer detail/loading + daemon-update prompt to reference design

Presentation-only reference-design migration:
- Explorer loading modal -> struct-form overlay (idSuffix explorerloading); block-
  detail modal loses its header divider; the search button + the prev/next nav
  become TactileButton; TR() the hardcoded "Previous block"/"Next block" tooltips,
  "TxID:", and the "shielded" output fallback (3 new explorer_* keys + reuse the
  existing `shielded` key), all 8 langs. Block-fetch RPC path untouched.
- Daemon-update startup prompt -> struct-form overlay (idSuffix daemonupdprompt),
  2 StyledButton -> TactileButton, drop the footer divider. The reinstall/
  prompted-size persistence logic is unchanged.

Build + ctest + hygiene clean; "DRGX" ticker left hardcoded per convention.

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

res/lang/ja.json

@@ -386,13 +386,16 @@
     "explorer_mempool": "メモリプール",
     "explorer_mempool_size": "サイズ",
     "explorer_mempool_txs": "トランザクション",
+    "explorer_next_block": "次のブロック",
     "explorer_no_results": "一致するキャッシュ済みブロックがありません",
     "explorer_not_connected": "デーモンに未接続 — ブロックまたはトランザクションハッシュを検索できません",
+    "explorer_prev_block": "前のブロック",
     "explorer_recent_blocks": "最近のブロック",
     "explorer_search": "検索",
     "explorer_section": "エクスプローラー",
     "explorer_tx_outputs": "出力",
     "explorer_tx_size": "サイズ",
+    "explorer_txid": "TxID：",
     "export": "エクスポート",
     "export_csv": "CSVエクスポート",
     "export_keys_btn": "鍵をエクスポート",