policy/v2: add SSH compatibility testdata from Tailscale SaaS
Add 39 test fixtures captured from Tailscale SaaS API responses
to validate SSH policy compilation parity. Each JSON file contains
the SSH policy section and expected compiled SSHRule arrays for 5
test nodes (3 user-owned, 2 tagged).
Test series: SSH-A (basic), SSH-B (specific sources), SSH-C
(destination combos), SSH-D (localpart), SSH-E (edge cases),
SSH-F (multi-rule), SSH-G (acceptEnv).
The data-driven TestSSHDataCompat harness uses cmp.Diff with
principal order tolerance but strict rule ordering (first-match-wins
semantics require exact order).
Updates #3049
6c59d3e601