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/board_input.h

@@ -0,0 +1,12 @@
+#ifndef BOARD_INPUT_H
+#define BOARD_INPUT_H
+
+#include "esp_err.h"
+
+/**
+ * Button (log on press) and LiPo ADC sampling (log every 10 s).
+ * TODO: Pin assignments come from powerpod.h and may not match final hardware yet.
+ */
+esp_err_t board_input_init(void);
+
+#endif