feat: SOS (experimental), issue #56: a countdown, then the position to chosen channels and contacts, repeated until someone answers

L1: Tools > SOS, Back held 3 s. L2: the SOS app, the top button held 5 s
opens a slider over everything, the lock screen and a PIN too. Off by default.
The ACK word stops the repeats; who answered, what they wrote and when show on
Answered, and whoever answered needs no word after that. Beep plays
... --- ... at full volume until it's ended. While one runs the screen goes off
by 30 s, the GPS stays awake past its duty cycle until nothing more will be
sent, the repeater and the L2's WiFi rest. A received SOS gets a banner and a
place on the map, past Track loc, for 24 h.

The lock screen's slider restyled with it, shared as slideBar() / slidePoll();
the L2's Favourites and SOS pickers share pickContacts(). The engine is
ui-core/SosEngine.h, tested on the host. The message's format isn't final.

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

examples/companion_radio/ui-lvgl/UITask.h

@@ -72,6 +72,7 @@ public:
   void onViewedHistoryGrew(bool channel) override { (void)channel; _thread_dirty = true; }
   void botSetGPS(bool on) override;
   void applySoundPrefs() override;
+  void onSosRunning(bool running) override;
   bool cliCommand(const char* command, char* reply, int n) override;
 
   // ── Navigation (called from LVGL event callbacks) ────────────────────────
@@ -315,6 +316,15 @@ public:
   void botToggle(int row, bool on);
   void botCmd(int id, bool on);
   void botGap(int idx);
+  void showSos();                        // SosScreen.h
+  void sosSheet();                       // the slider that starts one
+  void sosOpen();                        // the running one's view
+  void sosButton();                      // Cancel / Hide, or a physical button
+  void sosRow(int row);
+  void sosSet(int what, int val);
+  void sosChannel(int idx, bool on);
+  void sosContact(int idx);
+  void sosTextDone(bool ok);
   void botPick(int idx);
   void botHour(uint8_t act);
   void botTextDone(bool ok);
@@ -403,7 +413,7 @@ public:
   void statusBarSync();   // up or hidden, by the screen's title bar (UITask.cpp)
 
 private:
-  enum Screen : uint8_t { SCR_HOME, SCR_CHATS, SCR_CONTACTS, SCR_THREAD, SCR_SETTINGS, SCR_NEARBY, SCR_NODE, SCR_MAP, SCR_WIFI, SCR_SETTINGS_NAV, SCR_CLOCK, SCR_RADIO, SCR_CHANNEL_EDIT, SCR_ADMIN, SCR_BOT, SCR_DIAG, SCR_COMPASS, SCR_SCOPES, SCR_REPEATER, SCR_MELODY, SCR_QUICK, SCR_ADMIN_PICK, SCR_OTA, SCR_STORAGE, SCR_GPS, SCR_BATT, SCR_ROUTE, SCR_ROUTE_PICK, SCR_GALLERY };
+  enum Screen : uint8_t { SCR_HOME, SCR_CHATS, SCR_CONTACTS, SCR_THREAD, SCR_SETTINGS, SCR_NEARBY, SCR_NODE, SCR_MAP, SCR_WIFI, SCR_SETTINGS_NAV, SCR_CLOCK, SCR_RADIO, SCR_CHANNEL_EDIT, SCR_ADMIN, SCR_BOT, SCR_DIAG, SCR_COMPASS, SCR_SCOPES, SCR_REPEATER, SCR_MELODY, SCR_QUICK, SCR_ADMIN_PICK, SCR_OTA, SCR_STORAGE, SCR_GPS, SCR_BATT, SCR_ROUTE, SCR_ROUTE_PICK, SCR_GALLERY, SCR_SOS };
 
   void buildStatusBar();
   void refreshStatusBar();
@@ -540,6 +550,14 @@ private:
   void lockScreen();
   void refreshLock();
   void lockPoll();
+  bool sosViewOpen() const;
+  void sosViewClose();
+  void sosLive();
+  void sosRefresh();
+  void sosButtonHeld();
+  void sosPoll();
+  void sosTick();
+  void buildSos();
   void favGrid(lv_obj_t* grid);
   void favRefresh();
   int unreadTotal();   // DMs, channels and rooms
@@ -571,6 +589,7 @@ private:
   uint32_t _next_wake_poll_ms = 0;
   uint32_t _next_touch_poll_ms = 0;   // tap to wake, while the screen is off
   bool _wake_down = false;
+  uint32_t _wake_since_ms = 0;   // when the top button went down
   uint32_t autoOffMillis() const;
   uint32_t idleMillis(uint32_t lv_next);
   bool cpuNeeded();