sdk(P1.10): embedded parity self-test + attesto doctor

A trimmed (~1.7 KB) copy of the cross-language parity vectors now ships inside
each package (Python package-data JSON, Go go:embed, TS generated module). On
the first hashing operation per process each SDK recomputes the commitment
hash, the receipt domain-hash, and an inclusion fold against the vendored
vectors and fails closed (AttestoSelfTestError / ErrSelfTest) on any mismatch
— a corrupted install or diverging runtime can never silently produce wrong
evidence. Result is cached (including failure); cost <5 ms once. Corrupting a
vendored vector is test-asserted to fail closed in all three languages. The
frozen canonical primitives are untouched; the gate lives in the commitment/
verify entry points built on top of them.

attesto doctor: Go CLI subcommand and Python attesto.doctor(), producing a
deterministic {"ok", "checks"} report — vendored self-test, head-store
writability, number-policy dry-run on a sample payload, Ed25519 availability
(Python), and with credentials: reachability, protocol-header acceptance, and
clock skew vs the server Date header (warn >30 s; webhooks break at 300 s).

package_artifact_policy allows exactly attesto/_selftest_vectors.json in the
wheel (verified: built wheel contains it, policy green). READMEs updated.
This completes the last Phase-1 build item.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

proofstream.go

@@ -226,6 +226,9 @@ func assertSafeMap(m map[string]any, path string) error {
 // byte-identical to the server's stored payload_commitment. Call
 // AssertCommitmentSafeNumbers first if the payload is not yet known to be safe.
 func PayloadCommitment(payload any) (map[string]string, error) {
+	if err := EnsureSelfTest(); err != nil {
+		return nil, err
+	}
 	raw, err := CanonicalJSON(payload)
 	if err != nil {
 		return nil, err
@@ -503,6 +506,9 @@ func SignedConnectorWebhookHeaders(secret string, body []byte, timestamp int64)
 }
 
 func VerifyReceiptOffline(receipt SignedReceipt, publicKeyHex string) VerifyReport {
+	if err := EnsureSelfTest(); err != nil {
+		return VerifyReport{Kind: VerifyReceipt, OK: false, Problems: []string{err.Error()}}
+	}
 	problems := make([]string, 0)
 	hash, err := DomainHashHex(ProofstreamDomains["receipt"], receipt.Payload)
 	if err != nil {