Add board input driver for button and LiPo ADC logging.

TODO: Hardware pinning in powerpod.h (TASTER_GPIO, V_LIPO_1/2_GPIO) does not
match final hardware yet — verify against schematic before production.

Co-authored-by: Cursor <cursoragent@cursor.com>

main/powerpod.h

@@ -7,4 +7,13 @@
 #define I2C_PORT 0
 #define IO_EXPANDER_ADDRESS 0x20
 
+/* TODO: Hardware pinning not finalized — verify against schematic before production. */
+/** Front-panel button (active low, internal pull-up). */
+#define TASTER_GPIO 12
+
+/** LiPo voltage sense inputs (ADC1-capable GPIOs). */
+#define V_LIPO_1_GPIO 1
+/** Shares GPIO with TASTER on current bench wiring; second ADC is skipped in board_input.c. */
+#define V_LIPO_2_GPIO 12
+
 #endif