fix(eink): drive ringtone note advance from TIMER1 IRQ, not loop() poll

On nRF52 the buzzer advanced notes by polling millis() >= _note_end_ms in
loop(). A blocking display refresh (e-ink endFrame) starves loop(), so a
note boundary that falls inside a refresh is serviced late — the note
plays long, or the next is skipped. The keypress-time 300 ms render delay
only masked the first note.

Advance notes from a hardware TIMER1 compare interrupt instead, scheduled
for each note's exact duration, so timing is independent of render cadence.
TIMER0 is the SoftDevice's; TIMER1 is free (tone() uses PWM2, nrfx TIMER1
driver is disabled). loop() becomes a no-op on nRF52; the UITask keypress
render-delay workaround is removed.

_disarmNoteTimer() clears the latched NVIC pending IRQ (not just the event)
on stop()/_nrfBegin(), so a note-advance latched just before a stop can't
fire spuriously — which would skip a new melody's first note or blip after
an explicit stop. Event read-backs flush the write buffer per the nRF52
event anomaly.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

examples/companion_radio/ui-new/UITask.cpp

@@ -1995,18 +1995,10 @@ void UITask::loop() {
     if (!_locked && curr) {
       curr->handleInput(c);
       { uint32_t aoff = autoOffMillis(); if (aoff > 0) _auto_off = millis() + aoff; }  // extend auto-off timer
-#ifdef PIN_BUZZER
-      if (buzzer.isPlaying()) {
-        // Keep the next render at least 300 ms away so the blocking e-ink endFrame()
-        // doesn't extend the current note.  300 ms covers the slowest note at 120 BPM (1/4).
-        unsigned long deadline = millis() + 300;
-        if (_next_refresh < deadline) _next_refresh = deadline;
-      } else {
-        _next_refresh = 100;  // trigger refresh immediately
-      }
-#else
-      _next_refresh = 100;  // trigger refresh
-#endif
+      // Note timing no longer depends on render cadence (TIMER1 IRQ advances
+      // notes directly — see buzzer.cpp), so a redraw right after a keypress
+      // can't clip a note; no need to hold it back while buzzer.isPlaying().
+      _next_refresh = 100;  // trigger refresh immediately
     } else if (_locked) {
       // Locked: eat all keys — wake window is set only when display first turns on
       _next_refresh = 0;