feat(eink): suppress clock seconds to prevent per-second panel refreshes

E-ink panels take ~2 s for a full refresh and visible flicker on every update.
Showing seconds caused the clock page to redraw every 1 s, triggering a real
panel refresh each time the CRC changed.

- Default clock_hide_seconds=1 for EINK_DISPLAY_MODEL builds so fresh
  installs don't flicker out of the box.
- Remove the Seconds setting from SettingsScreen on e-ink so users can't
  accidentally re-enable it.
- Clock page now returns 60 s refresh interval on e-ink (content changes at
  most once per minute); other home pages capped at 30 s (new messages still
  force immediate redraw via notify()).
- Lock screen refresh interval raised from 1 s to 60 s on e-ink; button
  presses already reset _next_refresh=0, so unlock feedback is instant.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

examples/companion_radio/ui-new/UITask.cpp

@@ -692,11 +692,16 @@ public:
       }
     }
     bool auto_adv = _node_prefs && _node_prefs->advert_auto_interval_sec > 0;
+#ifdef EINK_DISPLAY_MODEL
+    if (_page == HomePage::CLOCK) return 60000;  // no seconds on e-ink; content changes at most every minute
+    return 30000;  // e-ink: limit base polling; new messages still force immediate refresh via notify()
+#else
     if (_page == HomePage::CLOCK) {
       bool show_sec = !_node_prefs || !_node_prefs->clock_hide_seconds;
       return auto_adv ? 1000 : (show_sec ? 1000 : 60000);
     }
     return auto_adv ? 1000 : 5000;
+#endif
   }
 
   bool handleInput(char c) override {
@@ -1399,7 +1404,11 @@ void UITask::loop() {
       _display->setCursor(hx, hy);
       _display->print(hint);
       _display->endFrame();
+#ifdef EINK_DISPLAY_MODEL
+      _next_refresh = millis() + 60000;
+#else
       _next_refresh = millis() + 1000;
+#endif
     } else if (!_locked && millis() >= _next_refresh && curr) {
       _display->startFrame();
       int delay_millis = curr->render(*_display);