feat(notsecrets): scaffold age-native domain types and trait ports

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

crates/notsecrets/src/recipients/mod.rs

@@ -0,0 +1,7 @@
+use crate::error::AgeError;
+use crate::identities::{FileKey, Stanza};
+
+/// Domain port: a recipient that can wrap a file key into a stanza.
+pub trait Recipient {
+    fn wrap_file_key(&self, file_key: &FileKey) -> Result<Stanza, AgeError>;
+}