feat(ui): rework the consolidate/merge modal

Make Merge to Address actually serve wallet-bloat consolidation and be far less
opaque. New ShieldDialog::showConsolidate() preset (used by the large-wallet
Settings banner + alert action) frames it as "Consolidate funds" and targets
shielded notes — the bloat the nudge warns about.

- Source selector: consolidate shielded notes (ANY_SAPLING), transparent
  (ANY_TADDR), or both (*) — previously hardcoded to ANY_TADDR, which never
  reduced the shielded-witness bloat. Batch limit now applies to the right side.
- Scope: on open, count spendable UTXOs + notes (listunspent / z_listunspent)
  and show "N transparent + M shielded · ~X DRGX"; warn "repeat to finish" when
  the set exceeds one batch.
- Destination auto-selects the best spendable z-address (button enabled by
  default); empty wallets get an inline "Create shielded address" (z_getnewaddress).
- Advanced disclosure hides Fee + "Max inputs per batch" (renamed from the "UTXO
  Limit" jargon) with sane defaults.
- Inline confirm step before the fund-moving call (amount + input count + dest).
- Live progress: self-polls z_getoperationstatus to show Consolidating… →
  Done/Failed, replacing the raw opid + manual "Check status" button.

All three merge entry points now use the typed showMerge()/showConsolidate()
(no stale-static leaks from direct show(MergeToAddress)). Shield-coinbase mode
keeps working. New i18n keys fall back to English.

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

src/app_network.cpp

@@ -4259,7 +4259,7 @@ void App::maybeWarnLargeWallet()
     settings_->save();
     ui::Notifications::instance().action(
         TR("wallet_size_warn"), ui::NotificationType::Warning,
-        []() { ui::ShieldDialog::show(ui::ShieldDialog::Mode::MergeToAddress); },
+        []() { ui::ShieldDialog::showConsolidate(); },
         TR("wallet_size_consolidate"), 12.0f);
 }