feat(recovery): import keys from a legacy wallet backup file (z_importwallet)

Phase 3: for a wallet.dat the current daemon can't open, recover its keys from the OLD wallet's export file.
Settings → "Import From Backup File…" opens a dialog that takes the path to a z_exportwallet / dumpwallet
dump (or SilentDragon's "Export all private keys") and calls z_importwallet — the daemon reads every key
and does ONE rescan, far faster and simpler than importing keys one at a time. On success it nudges the user
to shield any mined coinbase from the Shield screen.

- New App::importWalletFile(path, cb): runs z_importwallet on the long-call lane (no client timeout — the
  rescan can take a long time), then refreshAddresses + markWalletMutated. Full-node only.
- Only the PATH touches GUI memory, never the keys themselves (the daemon reads the file) — less secret
  exposure than a pasted-key field.
- New renderImportWalletFileDialog (typed path + Paste/Clear, progress, result) + a Settings card.

Reuses the existing long-call + z_importwallet infra; the careful single-key import dialog is untouched.
No send/sweep/encrypt call changed. Build + ctest green; the import/rescan itself is a daemon RPC, not
pure-testable, and wasn't exercised end-to-end here.

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

src/app.cpp

@@ -2582,7 +2582,11 @@ void App::render()
     if (show_import_key_) {
         renderImportKeyDialog();
     }
-    
+
+    if (show_import_wallet_file_) {
+        renderImportWalletFileDialog();
+    }
+
     if (show_export_key_) {
         renderExportKeyDialog();
     }
@@ -3949,6 +3953,85 @@ static void RenderScanHeightControl(char* buf, size_t bufSize, int tipHeight, bo
     ImGui::EndDisabled();
 }
 
+void App::renderImportWalletFileDialog()
+{
+    namespace m = ui::material;
+    float dp = ui::Layout::dpiScale();
+
+    m::OverlayDialogSpec ov;
+    ov.title     = TR("import_wallet_file_title");
+    ov.p_open    = &show_import_wallet_file_;
+    ov.style     = m::OverlayStyle::BlurFloat;
+    ov.cardWidth = 640.0f;
+    ov.idSuffix  = "importwalletfile";
+    if (!m::BeginOverlayDialog(ov)) return;
+
+    if (ImGui::IsWindowAppearing()) {
+        import_wallet_file_done_ = false;
+        import_wallet_file_ok_ = false;
+        import_wallet_file_status_.clear();
+    }
+    if (ImGui::IsKeyPressed(ImGuiKey_Escape) && !import_wallet_file_busy_) show_import_wallet_file_ = false;
+
+    m::DialogWarningHeader(TR("import_wallet_file_note"));
+    ImGui::Spacing();
+    if (!state_.connected) {
+        ImGui::TextColored(ImGui::ColorConvertU32ToFloat4(m::OnSurfaceMedium()), "%s", TR("import_key_need_node"));
+        ImGui::Spacing();
+    }
+
+    ImGui::TextUnformatted(TR("import_wallet_file_path_label"));
+    ImGui::SetNextItemWidth(ImGui::GetContentRegionAvail().x);
+    ImGui::BeginDisabled(import_wallet_file_busy_);
+    ImGui::InputText("##importwalletpath", import_wallet_file_path_, sizeof(import_wallet_file_path_));
+    ImGui::EndDisabled();
+
+    if (!import_wallet_file_busy_) {
+        if (m::TactileButton(TR("paste"), ImVec2(104 * dp, 0))) {
+            const char* clip = ImGui::GetClipboardText();
+            if (clip) {
+                std::string t = dragonx::util::trimmedClipboardText(clip);
+                snprintf(import_wallet_file_path_, sizeof(import_wallet_file_path_), "%s", t.c_str());
+            }
+        }
+        ImGui::SameLine();
+        if (m::TactileButton(TR("clear"), ImVec2(104 * dp, 0))) import_wallet_file_path_[0] = '\0';
+    }
+    ImGui::Spacing();
+
+    if (import_wallet_file_busy_) {
+        ImGui::TextColored(ImGui::ColorConvertU32ToFloat4(m::OnSurfaceMedium()), "%s%s",
+                           TR("import_wallet_file_importing"), m::LoadingDots());
+        ImGui::Spacing();
+    } else if (import_wallet_file_done_) {
+        ImGui::PushStyleColor(ImGuiCol_Text, ImGui::ColorConvertU32ToFloat4(
+            import_wallet_file_ok_ ? m::Success() : m::ReadableError()));
+        ImGui::TextWrapped("%s", import_wallet_file_status_.c_str());
+        ImGui::PopStyleColor();
+        ImGui::Spacing();
+    }
+
+    ImGui::BeginDisabled(import_wallet_file_busy_ || !state_.connected || import_wallet_file_path_[0] == '\0');
+    if (m::TactileButton(TR("import_wallet_file_import_btn"), ImVec2(190 * dp, 0))) {
+        import_wallet_file_busy_ = true;
+        import_wallet_file_done_ = false;
+        import_wallet_file_status_.clear();
+        importWalletFile(import_wallet_file_path_, [this](bool ok, const std::string& err) {
+            import_wallet_file_busy_  = false;
+            import_wallet_file_done_  = true;
+            import_wallet_file_ok_    = ok;
+            import_wallet_file_status_ = ok ? std::string(TR("import_wallet_file_ok")) : err;
+        });
+    }
+    ImGui::EndDisabled();
+    ImGui::SameLine();
+    ImGui::BeginDisabled(import_wallet_file_busy_);
+    if (m::TactileButton(TR("close"), ImVec2(110 * dp, 0))) show_import_wallet_file_ = false;
+    ImGui::EndDisabled();
+
+    m::EndOverlayDialog();
+}
+
 void App::renderImportKeyDialog()
 {
     namespace m = ui::material;