docs: publish password hashing APIs

site/doc/pages/password_hash.txt

@@ -0,0 +1,18 @@
+:sig
+String password_hash(String password)
+
+:params
+password : password bytes to hash
+return value : self-contained scrypt encoding, or an empty string on failure
+
+:content
+Creates a password credential with a cryptographically random salt and UCE's current bounded scrypt parameters. Store the returned encoding exactly as produced. An empty result means hashing failed; abort the credential write and report an operational error instead of storing it.
+
+:example
+String encoded = password_hash("correct horse battery staple");
+print(encoded != "" && password_verify("correct horse battery staple", encoded) ? "valid" : "failed", "\n");
+
+:see
+>sys
+password_verify
+password_needs_rehash