feat(mining): explain solo/pool, add a payout-address create path, surface the miner download

New-user mining cluster from the UX audit:
- Solo/Pool toggle: hover tooltips on each half explaining the trade-off
  (solo = no fees but long waits on a small CPU; pool = frequent small payouts,
  needs the miner + a shielded payout address).
- Payout field: when it's empty (new wallets have no z-address, and a pool
  payout must be shielded) the bookmark button is replaced by a one-click
  "Generate a shielded payout address" button (createNewZAddress → fills the
  field, persists, toasts), instead of only a hover hint to the Receive tab.
- Miner updater pill: when no miner is installed it becomes a prominent accent
  "Download miner" call-to-action with a "pool mining needs DRG-XMRig" tooltip,
  instead of a subtle grey "Update" pill that's easy to miss.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/util/i18n.cpp

@@ -2289,6 +2289,9 @@ void I18n::loadBuiltinEnglish()
         strings_["validate_mining_type"] = "Mining address (transparent)";
         strings_["mining_est_daily_pool_sub"] = "rough solo-equivalent, before pool fee";
         strings_["mining_generate_z_address_hint"] = "Generate a Z address in the Receive tab to use as your payout address";
+        strings_["mining_generate_z_address"] = "Generate a shielded payout address";
+        strings_["mining_generate_z_ok"] = "Created a shielded payout address.";
+        strings_["mining_generate_z_failed"] = "Couldn't create a shielded address — try the Receive tab.";
         strings_["mining_pool_needs_payout_tooltip"] = "Enter a payout address first (generate a Z address)";
         strings_["mining_pool"] = "Pool";
         strings_["mining_payout_foreign"] = "⚠ This payout address isn't in your current wallet — mined rewards would go to a different wallet. Update it if you switched wallets.";
@@ -2328,6 +2331,8 @@ void I18n::loadBuiltinEnglish()
         strings_["mining_starting_tooltip"] = "Miner is starting...";
         strings_["mining_stop"] = "Stop";
         strings_["mining_stop_solo_for_pool"] = "Stop solo mining before starting pool mining";
+        strings_["mining_solo_tip"] = "Solo: your node mines on its own. No pool fees, but a small CPU may wait a long time between rewards.";
+        strings_["mining_pool_tip"] = "Pool: team up with other miners for smaller, more frequent payouts. Needs the DRG-XMRig miner and a shielded payout address.";
         strings_["mining_stop_solo_for_pool_settings"] = "Stop solo mining to change pool settings";
         strings_["mining_stopping"] = "Stopping...";
         strings_["mining_stopping_tooltip"] = "Miner is stopping...";
@@ -2339,6 +2344,8 @@ void I18n::loadBuiltinEnglish()
 
         // --- Miner (xmrig) updater ---
         strings_["xmrig_update_button"]      = "Update miner…";
+        strings_["xmrig_download_miner"]     = "Download miner";
+        strings_["xmrig_download_miner_tip"] = "Pool mining needs the DRG-XMRig miner. Click to download and install it.";
         strings_["xmrig_update_short"]       = "Update";
         strings_["xmrig_releases"]           = "xmrig releases";
         strings_["xmrig_current"]            = "Current:";