The board lives in your GitHub repo. Every phone reads it and commits changes back — so everyone sees the same board. Two phones editing at once merge cleanly. Still works offline; catches up when there's signal.
One-time: GitHub → Settings → Developer settings → Fine-grained tokens → new token → Repository access = only wishwood-keeper-data → Permissions → Contents: Read and write → paste it above. Then Copy invite link and send it to the team — they just open it (the link carries the settings; keep it private).