Backs the tailscale_user and tailscale_users data sources. getUser maps
gorm/ErrUserNotFound to 404; unmodelled fields are honest constants,
deviceCount/lastSeen/currentlyConnected aggregate the user's nodes.
Tailscale's keys API has no separate expire verb: DELETE is the revoke.
Map it to a soft revoke so the key stays retrievable as invalid afterwards
instead of vanishing, matching the SDK and Terraform's expectations.
Add a revoked timestamp to pre-auth keys (migration plus schema), mark a
key invalid once revoked, and have the keys DELETE handler stamp it rather
than destroy the row. A background collector reaps revoked keys after a
configurable retention window (preauth_keys.revoked_retention, default
168h), so the table does not grow without bound.
Add the v2 foundation — Basic/Bearer auth, scope scaffolding, the
tailnet check, and the Tailscale error shape — plus the auth-key
endpoints mapped onto Headscale pre-auth keys.
Kristoffer Dalby