feat(lite): first-run welcome prompt (create / restore)

Replace the bare "land on main UI with a No-wallet overlay" first-run with a
lite welcome modal, shown when no wallet file exists yet (lite_wallet_ present,
not open, walletExists() false):

- "Create new wallet" — one-click createWallet({}); on success, notifies the user
  to back up their recovery phrase and navigates to Settings (Backup & keys),
  where the seed can be revealed/copied via the existing backup UI.
- "Restore from seed" — navigates to Settings (Lite wallet request → Restore).
- "Later" — dismiss for the session.

Routes to the already-built + verified create/restore/backup flows rather than
re-implementing seed display in the modal (no new secret-handling surface).
Dismissed once an action is chosen; never shown again once a wallet exists.
Full-node is unaffected (renderLiteFirstRunPrompt() returns early when
lite_wallet_ is null). English i18n built-ins added.

Verified: fresh-HOME lite launch shows the prompt, clean run + shutdown, no
crash/RPC noise; tests pass.

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

src/app.cpp

@@ -1394,7 +1394,10 @@ void App::render()
     if (show_about_) {
         ui::RenderAboutDialog(this, &show_about_);
     }
-    
+
+    // Lite first-run welcome: prompt to create/restore when no wallet file exists yet.
+    renderLiteFirstRunPrompt();
+
     if (show_import_key_) {
         renderImportKeyDialog();
     }
@@ -1785,6 +1788,61 @@ void App::reloadThemeImages(const std::string& bgPath, const std::string& logoPa
     coin_logo_h_ = 0;
 }
 
+void App::renderLiteFirstRunPrompt()
+{
+    // Lite-only: a brief welcome shown when no wallet file exists yet (full-node uses the wizard,
+    // which is skipped in lite). Routes to the existing create/restore + Backup flows in Settings.
+    if (!lite_wallet_ || lite_firstrun_dismissed_) return;
+    if (lite_wallet_->walletOpen() || lite_wallet_->walletExists()) return;
+
+    if (!ImGui::IsPopupOpen("##LiteFirstRun")) ImGui::OpenPopup("##LiteFirstRun");
+
+    ImGuiViewport* vp = ImGui::GetMainViewport();
+    ImGui::SetNextWindowPos(ImVec2(vp->Pos.x + vp->Size.x * 0.5f, vp->Pos.y + vp->Size.y * 0.5f),
+                            ImGuiCond_Appearing, ImVec2(0.5f, 0.5f));
+    if (ImGui::BeginPopupModal("##LiteFirstRun", nullptr,
+                               ImGuiWindowFlags_AlwaysAutoResize | ImGuiWindowFlags_NoTitleBar)) {
+        ImGui::PushFont(ui::material::Type().subtitle1());
+        ImGui::TextUnformatted(TR("lite_welcome_title"));
+        ImGui::PopFont();
+        ImGui::Spacing();
+        ImGui::PushTextWrapPos(ImGui::GetCursorPosX() + 360.0f);
+        ImGui::TextUnformatted(TR("lite_welcome_msg"));
+        ImGui::PopTextWrapPos();
+        ImGui::Spacing();
+        ImGui::Spacing();
+
+        const float btnW = 170.0f;
+        if (ImGui::Button(TR("lite_welcome_create"), ImVec2(btnW, 0))) {
+            // One-click create (unencrypted by default); the user backs up the seed next via the
+            // Settings → Backup & keys flow, where the seed can be revealed and copied.
+            const auto result = lite_wallet_->createWallet(wallet::LiteWalletCreateRequest{});
+            if (result.walletReady) {
+                ui::Notifications::instance().success(TR("lite_welcome_created"), 8.0f);
+                setCurrentPage(ui::NavPage::Settings);
+            } else {
+                ui::Notifications::instance().warning(TR("lite_welcome_create_failed"));
+            }
+            lite_firstrun_dismissed_ = true;
+            ImGui::CloseCurrentPopup();
+        }
+        ImGui::SameLine();
+        if (ImGui::Button(TR("lite_welcome_restore"), ImVec2(btnW, 0))) {
+            ui::Notifications::instance().info(TR("lite_welcome_restore_hint"), 8.0f);
+            setCurrentPage(ui::NavPage::Settings);
+            lite_firstrun_dismissed_ = true;
+            ImGui::CloseCurrentPopup();
+        }
+        ImGui::Spacing();
+        if (ImGui::Button(TR("lite_welcome_later"),
+                          ImVec2(btnW * 2 + ImGui::GetStyle().ItemSpacing.x, 0))) {
+            lite_firstrun_dismissed_ = true;
+            ImGui::CloseCurrentPopup();
+        }
+        ImGui::EndPopup();
+    }
+}
+
 void App::renderAboutDialog()
 {
     auto dlg = ui::schema::UI().drawElement("inline-dialogs", "about");