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

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

crates/notsecrets/src/error.rs

@@ -0,0 +1,15 @@
+#[derive(Debug, thiserror::Error)]
+pub enum AgeError {
+    #[error("no identity could decrypt any recipient stanza")]
+    NoMatch,
+    #[error("header MAC verification failed")]
+    MacMismatch,
+    #[error("malformed age file: {0}")]
+    ParseError(String),
+    #[error("crypto error: {0}")]
+    CryptoError(String),
+    #[error("unsupported key type: {0}")]
+    UnsupportedKeyType(String),
+    #[error("identity source failed ({name}): {source}")]
+    SourceError { name: String, source: anyhow::Error },
+}