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/services/wallet_security_controller.h

@@ -74,6 +74,9 @@ public:
                                                 std::size_t minLength = 4);
     static KeyKind classifyAddress(const std::string& address);
     static KeyKind classifyPrivateKey(const std::string& key);
+    // True if `key` looks like a recognized Z (Sapling/Sprout spending) or T (WIF) private key.
+    // Single source of truth for the import dialog's indicator AND its submit guard.
+    static bool isRecognizedPrivateKey(const std::string& key);
     static const char* importSuccessMessage(KeyKind kind);
     static std::string decryptExportFileName(std::uint64_t timestampSeconds);
     static void secureClear(std::string& value);