fix(eink): capture button edges via GPIO interrupt to survive display refresh

E-ink panel refreshes block the main loop for 500ms-3.6s (GxEPD2's
display.display() waits on the BUSY pin), and MomentaryButton::check()
only ever samples the live pin level once per loop iteration. A full
press+release that lands entirely inside a refresh is never sampled,
not just delayed - users on WioTracker L1 Eink were losing taps.

Add an opt-in ISR path (BUTTON_USE_INTERRUPTS) that latches each edge
with its own timestamp into a small ring buffer from attachInterrupt(),
independent of what the main loop is doing. check() replays buffered
edges through the existing transition/multi-click logic afterwards, so
click-duration and multi-click-window math still uses the edge's actual
capture time rather than "now".

Scoped to wio-tracker-l1-eink only for now: it's the one board this was
reported against and the only GxEPDDisplay-class variant that currently
builds clean on main. OLED boards refresh in ~20-30ms so polling already
catches every press; analog-button boards (rak4631/rak3401) can't use
attachInterrupt(CHANGE) at all.

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

variants/wio-tracker-l1-eink/platformio.ini

@@ -29,6 +29,7 @@ build_flags = ${nrf52_base.build_flags}
   -D MAX_GROUP_CHANNELS=40
   -D OFFLINE_QUEUE_SIZE=256
   -D DISPLAY_CLASS=GxEPDDisplay
+  -D BUTTON_USE_INTERRUPTS=1
   -D UI_HAS_JOYSTICK=1
   -D UI_HAS_JOYSTICK_UPDOWN=1
   -D PIN_BUZZER=12