chore(secrets): placeholder for the LDAP bind secret

secrets/ldap-bind.age.PLACEHOLDER

@@ -0,0 +1,21 @@
+THIS IS A PLACEHOLDER, NOT A REAL AGE SECRET.
+
+The real secrets/ldap-bind.age is produced by the repo owner with `agenix -e`
+(see secrets/README.md) and is a binary age-encrypted blob. It is intentionally
+NOT committed here because:
+  * the real host age recipients are not available to the author of this change
+    (they are each host's /etc/ssh/ssh_host_ed25519_key.pub), and
+  * fabricating an encrypted blob or fake host keys would be misleading.
+
+Committing this file as `ldap-bind.age` would let modules/sssd.nix reference
+`../secrets/ldap-bind.age` and evaluate, but SSSD would fail to decrypt it at
+runtime. Do ONE of the following before deploying:
+
+  1. Preferred: generate the real secret (secrets/README.md), commit it as
+     secrets/ldap-bind.age, and delete this .PLACEHOLDER file.
+
+The decrypted plaintext must be a valid sssd.conf drop-in (NOT the bare
+password):
+
+    [domain/default]
+    ldap_default_authtok = <the sssd-bind service-account password>