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.h

@@ -425,6 +425,8 @@ private:
     // One-shot guard: auto-open an existing lite wallet on the first update() tick (kept off
     // init() so a slow initialize_existing network call doesn't freeze startup before the window).
     bool lite_autoopen_done_ = false;
+    // Lite first-run welcome prompt: dismissed for the session once the user picks an action.
+    bool lite_firstrun_dismissed_ = false;
     std::unique_ptr<daemon::DaemonController> daemon_controller_;
     std::unique_ptr<daemon::XmrigManager> xmrig_manager_;
     util::AsyncTaskManager async_tasks_;
@@ -648,6 +650,7 @@ private:
     // Private methods - rendering
     void renderStatusBar();
     void renderAboutDialog();
+    void renderLiteFirstRunPrompt();  // lite-only welcome modal when no wallet exists yet
     void renderImportKeyDialog();
     void renderExportKeyDialog();
     void renderBackupDialog();