docs: note cryptbin credential-binding requirements

Document that new cryptbin items can enforce creating-credential binding for unwrap/update/delete operations in addition to key proof.

README.md

@@ -145,6 +145,7 @@ This wrapper now delegates to `BlackWall\Auth\AuthClient`.
 - Never place client secrets, refresh tokens, or access tokens in URL query strings.
 - For OIDC providers, include a per-request `nonce` in authorisation requests.
 - For direct Cryptbin API usage, send `key_b64url` on unwrap calls; provider rejects key-mismatch unwrap attempts with `403 Forbidden`.
+- For newly created Cryptbin items, continue using the creating WebAuthn credential for unwrap/update/delete flows.
 - Always use HTTPS in production.
 - Store refresh tokens securely.
 - Keep access tokens out of logs and browser-visible output.

docs/INTEGRATION_GUIDE.md

@@ -173,3 +173,4 @@ Provider user/project assignment views may exclude disabled projects even if his
 - HTTPS URLs are enforced by default in `Config::fromArray()`.
 - For localhost-only HTTP testing, explicitly set `allowInsecureHttp => true`.
 - If you call Cryptbin unwrap APIs directly, include the original share key as `key_b64url`; unwrap now returns `403 Forbidden` when key proof does not match metadata verifier.
+- New Cryptbin items may also bind unwrap/update/delete operations to the creating WebAuthn credential; use the same authenticator for follow-up operations.