feat(ui): treat transparent addresses as mining-only addresses

DragonX is a private chain (-ac_private=1): consensus rejects any
non-coinbase output to a transparent address, so a t-address can only
ever receive mining rewards, and its coins can only move to a shielded
address. The wallet treated them like ordinary recipients.

Block paying one:
- Send: a transparent recipient shows "Mining address - can't be paid"
  and disables Review Send (tooltip explains; ask for a zs... address).
  Typing, paste, contacts and payment URIs all go through this field.
- Overview drag-to-transfer: a mining-address row is never a transfer
  target (it only reorders).
- Pool payout must be shielded (pools pay with ordinary transactions):
  field tooltip, disabled Start button and the start check say why.
- isValidRecipientAddress() is now shielded-only; new isDragonXAddress()
  and classifyRecipient() (Shielded / MiningOnly / Invalid).

Call them mining addresses:
- Overview: "Mining rewards" card (amber "Not yet shielded" when there
  is a balance; hover explains; click opens the Shield dialog), "New
  mining address" button with a tooltip, rows typed "Mining".
- QR / label dialogs, portfolio filter, contact badge ("Mining only"),
  Receive notifications.

i18n: 17 new keys in all 8 languages, 12 dead keys removed, CJK subset
rebuilt. Tests: recipient classification, translation completeness.
UI sweep: new "send-mining-recipient" target.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/app_sweep.cpp

@@ -588,6 +588,11 @@ void App::buildSweepCatalog()
         [](App& a) { a.state_.connected = false; a.state_.encryption_state_known = false; },
         [](App& a) { a.applyHealthyDemoState(); });
 
+    // A mining (transparent) address as the recipient: shown as unpayable, Send disabled.
+    add("send-mining-recipient", ui::NavPage::Send,
+        [](App& a) { ui::SweepSetSendRecipient(&a, "R9NXAVJezHiBnT3ijTpg3JUZre7PxhJWti"); },
+        [](App& a) { ui::SweepSetSendRecipient(&a, nullptr); });
+
     // Send-confirm popup (state lives in send_tab statics → driven via a debug hook).
     add("popup-send-confirm", ui::NavPage::Send,
         [](App& a) { ui::SweepShowSendConfirm(&a, true); },