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/bootstrap_download_dialog.h

@@ -30,8 +30,15 @@ class BootstrapDownloadDialog {
 public:
     static void show(App* app) {
         if (!app || !app->supportsFullNodeLifecycleActions()) return;
-        s_open = true;
         s_app = app;
+        // If a download is already in flight, RE-ATTACH to it (just reopen showing progress) instead of
+        // resetting state and orphaning the running worker / restarting an unverified download.
+        if (app->isBootstrapDownloading()) {
+            s_open = true;
+            if (s_state == State::Confirm) s_state = State::Downloading;
+            return;
+        }
+        s_open = true;
         s_state = State::Confirm;
         s_bootstrap.reset();
         s_errorMsg.clear();