Completed full KiCad 8 schematic and 2-layer PCB layout for the 4x4 XIAO RP2040 switch matrix with 1N4148 SOD-123 column diodes, EC11 encoder, and SSD1306 I2C OLED header. Exported 3mm top switch plate and 13mm bottom case STL/STEP geometry with M3x5x4mm heatset insert bosses, plus runnable KMK/CircuitPython firmware and browser keymap verifier.