HAL: add PWR long-press + release edges to power_hal

Adds power_hal_pwr_long_pressed() and power_hal_pwr_released() to the HAL
contract so shared code can implement a hold-to-pair gesture board-agnostically.

- 216: enable the AXP2101 PKEY LONG + POSITIVE IRQs; bump press-off to 8s so a
  ~3-6s pair hold doesn't trip the hardware shutdown.
- 1.8": synthesize the same long/release edges in software from the polled
  XCA9554 EXIO4 level (short-press now fires on release-if-short).
- template: stub the two new functions (no gesture) for new ports.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

firmware/src/hal/power_hal.h

@@ -17,3 +17,11 @@ bool power_hal_is_vbus_in(void);   // USB cable present (true even without a bat
 
 // Edge-triggered: returns true once per PWR short-press, then clears.
 bool power_hal_pwr_pressed(void);
+
+// Edge-triggered: true once when a PWR hold crosses the long-press threshold
+// (~1.5s), then clears. Starts the hold-to-pair gesture.
+bool power_hal_pwr_long_pressed(void);
+
+// Edge-triggered: true once on the PWR release edge, then clears. Completes
+// or cancels the hold-to-pair gesture.
+bool power_hal_pwr_released(void);