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/shield_dialog.cpp

@@ -166,9 +166,12 @@ void ShieldDialog::render(App* app)
             ImGui::Spacing();
         }
 
-        // Buttons
-        bool can_submit = !s_operation_pending && s_to_address[0] != '\0';
-        
+        // Buttons — guard on connection/sync like the Send tab (a disconnected or mid-sync submit just
+        // fails at the daemon with a raw error).
+        bool sh_connected = app->isConnected();
+        bool sh_syncing   = state.sync.syncing;
+        bool can_submit = !s_operation_pending && s_to_address[0] != '\0' && sh_connected && !sh_syncing;
+
         if (!can_submit) ImGui::BeginDisabled();
         
         const char* btn_label = (s_mode == Mode::ShieldCoinbase) ? TR("shield_funds") : TR("merge_funds");
@@ -244,7 +247,12 @@ void ShieldDialog::render(App* app)
         }
         
         if (!can_submit) ImGui::EndDisabled();
-        
+        if (!can_submit && ImGui::IsItemHovered(ImGuiHoveredFlags_AllowWhenDisabled)) {
+            if (!sh_connected)              material::Tooltip("%s", TR("send_tooltip_not_connected"));
+            else if (sh_syncing)           material::Tooltip("%s", TR("send_tooltip_syncing"));
+            else if (s_to_address[0]=='\0') material::Tooltip("%s", TR("shield_select_z"));
+        }
+
         ImGui::SameLine();
         
         if (material::StyledButton(TR("cancel"), ImVec2(cancelBtn.width, 0), S.resolveFont(cancelBtn.font))) {