Setup

Read the Hack Club Hackpad guide and chose a 3-key design to learn on first.
Installed KiCad as an AppImage, with a launcher.
Added the Hack Club XIAO and SK6812 symbol libraries and the footprint library.

Schematic and PCB (KiCad)

Drew the schematic: a XIAO and three switches on D10, D9 and D8, each also going to GND.
Assigned footprints: MX switch footprints and the XIAO footprint.
Imported the parts into the PCB editor, flipped the XIAO to the back, spaced the switches 19.05 mm apart and routed all the traces.
Fixed a split ground connection.
Drew the board outline on Edge.Cuts (65 × 64 mm) and ran the DRC.

Case

Built a tray (85.8 × 84.8 mm, 13 mm tall, 3 mm floor) and a switch plate with three 14 mm holes in Onshape, after fixing the inch and millimeter problem.
Generated both parts as STEP files with a CadQuery script, then added a USB notch in the back wall.
Built one assembled hackpad.step, with a blank PCB inside, for the CAD folder.

Firmware

Wrote the KMK main.py for the three pins.

Production files and repo

Arranged the project into CAD, PCB, Firmware, production and images.
Exported the gerbers and drill files into gerbers.zip.
Took the screenshots, wrote README.md and bom.csv, and pushed everything to github.com/ema-rauf/hackpad.