No project uses floating-point, so coprocessor_enable() was dead code. Removes rp2350_coprocessor.c/.h and all references from reset handlers and Makefiles across all 15 CBM drivers (0x01-0x0f).
- GPIO15 active-low button input with internal pull-up - 20ms software debounce via busy-wait confirmation - LED mirrors button state, UART reports edge transitions - New gpio_config_input_pullup() in GPIO driver - 1555B FLASH, 13 source files, zero warnings