fix(ui-lvgl): no USB drive behind the screen PIN; drop the NVS PIN migration

The SD card (message history) could be lent to a computer from the lock
card before the PIN was entered. While locked with a PIN, usbPoll() no
longer reacts; a cable plugged in meanwhile is offered once unlocked.

The plain-text NVS PIN never shipped, so there's nothing to migrate.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

examples/companion_radio/ui-lvgl/LvglPort.h

@@ -680,7 +680,6 @@ static int  getU8(const char* ns, const char* key, int def) { return getInt(ns,
 static void putU8(const char* ns, const char* key, int v) { putInt(ns, key, v); }
 static void getStr(const char* ns, const char* key, char* out, size_t n) { Kv* k = find(ns, key, false); snprintf(out, n, "%s", k ? k->val : ""); }
 static void putStr(const char* ns, const char* key, const char* v) { if (Kv* k = find(ns, key, true)) snprintf(k->val, sizeof(k->val), "%s", v); }
-static void remove(const char* ns, const char* key) { if (Kv* k = find(ns, key, false)) k->val[0] = '\0'; }
 }  // namespace nvs
 
 static bool s_swallow = false;
@@ -849,12 +848,6 @@ static bool vectorOn() { return nvs::getBool("mc_ui", "vector", false); }
 static void setVectorOn(bool on) { nvs::putBool("mc_ui", "vector", on); }
 
 // Screen-lock PIN (Settings > Display & power > Screen PIN): digits, "" = none.
-// The screen PIN as older builds kept it (plain text): read once and removed;
-// it lives hashed in NodePrefs now (ui-core/ScreenLock.h).
-static void takeOldPin(char* out, size_t n) {
-  nvs::getStr("mc_lock", "pin", out, n);
-  if (out[0]) nvs::remove("mc_lock", "pin");
-}
 
 // Accent colour (Settings > Display & power): an index into theme::ACCENTS.
 static int loadAccent() { return nvs::getU8("mc_ui", "accent", 0); }

examples/companion_radio/ui-lvgl/StorageScreen.h

@@ -482,6 +482,9 @@ void UITask::usbPoll() {
     restartScreen("The computer has given the SD card back.");
     return;
   }
+  // Behind a screen PIN the card (message history) isn't offered: a cable
+  // plugged in while locked is noticed once the PIN is entered.
+  if (locked() && pinSet()) return;
   bool host = lvport::usbHost();
   if (host == s_host) return;
   s_host = host;
@@ -499,7 +502,7 @@ void UITask::usbPoll() {
 void UITask::usbTap(bool drive) {
   using namespace usbview;
   if (s_overlay) { lv_obj_delete_async(s_overlay); s_overlay = nullptr; }
-  if (!drive) return;
+  if (!drive || (locked() && pinSet())) return;
   storeview::stopWalk();
   if (mapview::s_dl.active()) mapDownloadStop();
   if (!lvport::usbDriveStart()) { showToast("No SD card to share", 3000); return; }

examples/companion_radio/ui-lvgl/UITask.cpp

@@ -898,14 +898,6 @@ void UITask::begin(DisplayDriver* display_drv, SensorManager* sensors, NodePrefs
   buildStatusBar();
   applyDisplayPrefs();   // a slider percentage overrides the level main.cpp set
   showHome();
-  // Before the PIN moved into NodePrefs it was kept in NVS in plain text.
-  char old_pin[9];
-  lvport::takeOldPin(old_pin, sizeof(old_pin));
-  if (old_pin[0] && _prefs && !pinSet()) {
-    screenlock::set(*_prefs, old_pin, the_mesh.getRNG());
-    the_mesh.savePrefs();
-  }
-  memset(old_pin, 0, sizeof(old_pin));
   if (pinSet()) lockScreen();   // a reboot doesn't get round the PIN
   showSplash();                // over both; fades out by itself
 }