feat(ui-lvgl): several saved WiFi networks, joined by signal; Save checks the password

- Settings > WiFi keeps up to 8 networks (NVS "s0".."s7" / "p0".."p7"; the
  single one older builds saved moves over). A tap loads one to change its
  password, Forget asks with a second tap, a scan marks the known ones.
- Map downloads, live tiles and updates join the strongest saved network in
  range (a short scan first when more than one is saved), else the newest
  one -- which also covers a hidden network.
- Save joins the network once: "password OK", turned away (forgotten again,
  the form keeps it to fix) or not in range (kept, checked later).

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

examples/companion_radio/ui-lvgl/UITask.h

@@ -119,6 +119,9 @@ public:
   void wifiSetAllowed(bool on);
   void wifiScan();
   void wifiPick(int idx);
+  void wifiOpenSaved(int idx);   // a saved network into the fields, to change its password
+  void wifiTestShow(const char* msg, const char* ssid, const char* pass);   // a password check's outcome
+  void wifiForget(int idx);      // (its button asks first: WifiScreen.h)
   void wifiSave();
   void wifiEdit(lv_obj_t* ta);
   void wifiKeyboardHide();