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/ui/windows/mining_mode_toggle.cpp

@@ -413,7 +413,10 @@ void RenderMiningModeToggle(App* app, const WalletState& state, const MiningInfo
                 if (currentWorkerStr.empty()) {
                     material::Tooltip("%s", TR("mining_generate_z_address_hint"));
                 } else if (currentWorkerStr != "x" && !util::isValidRecipientAddress(currentWorkerStr)) {
-                    material::Tooltip("%s", TR("mining_payout_invalid"));   // block start below too (M-01)
+                    // Block start below too (M-01). A pool pays with ordinary transactions, which can't reach
+                    // a transparent (mining) address on this private chain: say so rather than "invalid".
+                    material::Tooltip("%s", util::isTransparentAddress(currentWorkerStr)
+                                                ? TR("mining_payout_needs_shielded") : TR("mining_payout_invalid"));
                 } else {
                     material::Tooltip("%s", TR("mining_payout_tooltip"));
                 }