API keys, pre-auth keys and OAuth clients/tokens share one table and verify
path. Secrets carry 256 bits of crypto/rand entropy, so a SHA-256 digest
needs no stretching; bcrypt/argon2id rows rehash on use until 0.32.
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.