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/SettingsScreen.h

@@ -12,7 +12,9 @@ class SettingsScreen : public UIScreen {
     AUTO_OFF,
     AUTO_LOCK,
     BATT_DISPLAY,
+#if !defined(EINK_DISPLAY_MODEL)
     CLOCK_SECONDS,
+#endif
     CLOCK_FORMAT,
     FONT,
 #if defined(EINK_DISPLAY_MODEL)
@@ -312,10 +314,12 @@ class SettingsScreen : public UIScreen {
       display.setCursor(VAL_X, y);
       uint8_t mode = p ? p->batt_display_mode : 0;
       display.print(BATT_DISPLAY_LABELS[mode < BATT_DISPLAY_COUNT ? mode : 0]);
+#if !defined(EINK_DISPLAY_MODEL)
     } else if (item == CLOCK_SECONDS) {
       display.print("Seconds");
       display.setCursor(VAL_X, y);
       display.print((p && p->clock_hide_seconds) ? "OFF" : "ON");
+#endif
     } else if (item == CLOCK_FORMAT) {
       display.print("Format");
       display.setCursor(VAL_X, y);
@@ -512,11 +516,13 @@ public:
       if (left)  idx = (idx + BATT_DISPLAY_COUNT - 1) % BATT_DISPLAY_COUNT;
       if (left || right) { p->batt_display_mode = idx; _dirty = true; return true; }
     }
+#if !defined(EINK_DISPLAY_MODEL)
     if (_selected == CLOCK_SECONDS && p && (left || right || enter)) {
       p->clock_hide_seconds ^= 1;
       _dirty = true;
       return true;
     }
+#endif
     if (_selected == CLOCK_FORMAT && p && (left || right || enter)) {
       p->clock_12h ^= 1;
       _dirty = true;