Portainer's git-stack checkout does not materialize sibling repo files
at the relative bind path, so ./serve-roms.json mounted as an empty
auto-created directory and tailscale serve failed ('is a directory').
Switch to an absolute /config/share/serve-roms.json bind (matching every
other stack's /config convention); the file is mirrored on the host.
Adds stacks/share/ — a dedicated stack of userspace Tailscale 'serve'
nodes that expose individual internal services to external tailnet
users (a friend on his own tailnet) over each node's 100.x identity.
No public exposure, no LAN access, immune to the friend's home-subnet
addressing. First node ts-roms serves RomM at roms-share.<tailnet>.ts.net
-> romm:8080. One reusable tag:share auth key + one ACL rule cover every
node; adding a service is a serve-<svc>.json + a copied service block.
roms stack reverted to a pointer comment.
ginnoir