fix: Tier-2 UX robustness — action guards, in-progress guards, input trimming

The app-wide "import-key pattern" fixes (missing guards / untrimmed input / no
re-entrancy protection), from the robustness audit:

- Import-key dialog: unify the type indicator and the RPC dispatch on one
  classifier (classifyPrivateKey is now prefix-aware — an "SK..." shielded key no
  longer misroutes to the transparent RPC), trim manual input (not just Paste),
  and gate both the indicator and the Import button on a shared
  isRecognizedPrivateKey() so unrecognized/empty input can't be submitted.
- Shield: guard the submit button on connected + !syncing (like Send), with a
  disabled tooltip, instead of firing into a raw daemon error.
- Mining: disable the pool Mine button when the payout address is empty
  ("enter a payout address first"), and trim the pool URL/worker on persist.
- Console: track in-flight RPC commands (atomic counter + busy() override) so the
  input is disabled while a command runs instead of piling up on the worker.
- Maintenance (rescan/repair/delete-chain/reinstall-daemon): re-entrancy guard —
  bail with "already in progress" instead of launching a duplicate destructive op.
- Bootstrap dialog: re-attach to an in-flight download on reopen instead of
  resetting state and orphaning the running worker.

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

src/ui/windows/mining_controls.cpp

@@ -690,8 +690,12 @@ void RenderMiningControls(App* app, const WalletState& state, const MiningInfo&
             // If pool mining is still shutting down after switching to solo,
             // keep the button enabled so user can stop it.
             bool poolStillRunning = !s_pool_mode && state.pool_mining.xmrig_running;
+            // Can't start pool mining without a payout address (blank for a new wallet with no z-address);
+            // only blocks starting — stopping a running miner stays enabled.
+            bool poolNeedsPayout = s_pool_mode && !state.pool_mining.xmrig_running &&
+                                   std::string(s_pool_worker).empty();
             bool disabled = s_pool_mode
-                ? (isToggling || poolBlockedBySolo)
+                ? (isToggling || poolBlockedBySolo || poolNeedsPayout)
                 : (poolStillRunning ? false : (!app->isConnected() || isToggling || isSyncing));
 
             // Glass panel background with state-dependent tint
@@ -821,6 +825,8 @@ void RenderMiningControls(App* app, const WalletState& state, const MiningInfo&
                     material::Tooltip(TR("mining_syncing_tooltip"), state.sync.verification_progress * 100.0);
                 else if (poolBlockedBySolo)
                     material::Tooltip("%s", TR("mining_stop_solo_for_pool"));
+                else if (poolNeedsPayout)
+                    material::Tooltip("%s", "Enter a payout address first (generate a Z address)");
                 else
                     material::Tooltip("%s", isMiningActive ? TR("stop_mining") : TR("start_mining"));
             }