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/fr.json

@@ -386,13 +386,16 @@
     "explorer_mempool": "Mempool",
     "explorer_mempool_size": "Taille",
     "explorer_mempool_txs": "Transactions",
+    "explorer_next_block": "Bloc suivant",
     "explorer_no_results": "Aucun bloc en cache correspondant",
     "explorer_not_connected": "Non connecté au daemon — impossible de rechercher un hash de bloc ou de transaction",
+    "explorer_prev_block": "Bloc précédent",
     "explorer_recent_blocks": "Blocs récents",
     "explorer_search": "Rechercher",
     "explorer_section": "EXPLORATEUR",
     "explorer_tx_outputs": "Sorties",
     "explorer_tx_size": "Taille",
+    "explorer_txid": "TxID :",
     "export": "Exporter",
     "export_csv": "Exporter en CSV",
     "export_keys_btn": "Exporter les clés",