Tailscale validates that autogroup:self destinations in ACL rules can
only be used when ALL sources are users, groups, autogroup:member, or
wildcard (*). Previously, Headscale only performed this validation for
SSH rules.
Add validateACLSrcDstCombination() to enforce that tags, autogroup:tagged,
hosts, and raw IPs cannot be used as sources with autogroup:self
destinations. Invalid policies like `tag:client → autogroup:self:*` are
now rejected at validation time, matching Tailscale behavior.
Wildcard (*) is allowed because autogroup:self evaluation narrows it
per-node to only the node's own IPs.
Updates #3036
ebdbe03639