security: scrub on-screen secrets on lock; redact lite console secret args; no-shell wallet rebuild

- Locking the wallet (manual / auto / lite) now calls wipeDisplayedSecrets(),
  which scrubs + closes any revealed seed phrase, migration seed, or exported
  key — previously a locked wallet could leave the phrase/key on screen and
  resident. Runs synchronously, before the async lock round-trip.
- The console secret-arg redaction list only had full-node RPC names, so lite
  verbs (import / timport / encrypt / decrypt / unlock) echoed keys and
  passphrases into the scrollback and up-arrow history; added them.
- The offline wallet-rebuild helper was invoked via a shell string
  (popen "sh -c") built from paths including the wallet filename, so a crafted
  name could inject a command; it now refuses any path with a shell
  metacharacter (rc stays -1 and the existing verify-before-swap fails safe).

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

src/app.cpp

@@ -145,6 +145,25 @@ void App::wipeSecrets()
     sodium_memzero(import_clip_preview_, sizeof(import_clip_preview_)); // clipboard preview (SECRET)
 }
 
+// Scrub + close any secret that is currently ON SCREEN (revealed seed phrase, migration seed, exported
+// key) when the wallet locks — locking shouldn't leave a phrase/key visible or resident. Called on every
+// lock transition (manual, auto, lite). Separate from wipeSecrets(), which is the exit-path scrub.
+void App::wipeDisplayedSecrets()
+{
+    if (!seed_backup_phrase_.empty()) {
+        sodium_memzero(&seed_backup_phrase_[0], seed_backup_phrase_.size());
+        seed_backup_phrase_.clear();
+    }
+    if (!seed_migration_seed_.empty()) {
+        sodium_memzero(&seed_migration_seed_[0], seed_migration_seed_.size());
+        seed_migration_seed_.clear();
+    }
+    seed_backup_fetch_started_ = false;
+    show_seed_backup_ = false;
+    sodium_memzero(export_result_, sizeof(export_result_));
+    ui::KeyExportDialog::hide();   // zeros its static s_key via secureWipeLiteSecret
+}
+
 // Enqueue a blocking xmrig start/stop op onto the dedicated serialized control thread so the render thread
 // never blocks on stop()'s SIGTERM->SIGKILL->join, while start/stop still execute in FIFO order. (M-03/…)
 void App::postMiningControl(std::function<void()> job)