feat(core): flesh out IdentityCore

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

crates/idfoto-core/src/item_types/identity.rs

@@ -1,3 +1,45 @@
+//! Identity: name, address, phone, email, date-of-birth.
+
+use chrono::NaiveDate;
 use serde::{Deserialize, Serialize};
+
 #[derive(Debug, Clone, Serialize, Deserialize, Default)]
-pub struct IdentityCore {}
+pub struct IdentityCore {
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub full_name: Option<String>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub address: Option<String>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub phone: Option<String>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub email: Option<String>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub date_of_birth: Option<NaiveDate>,
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn identity_full_round_trip() {
+        let id = IdentityCore {
+            full_name: Some("Alice Doe".into()),
+            address: Some("123 Main St\nAnytown".into()),
+            phone: Some("+1-555-0100".into()),
+            email: Some("alice@example.com".into()),
+            date_of_birth: NaiveDate::from_ymd_opt(1990, 4, 18),
+        };
+        let json = serde_json::to_string(&id).unwrap();
+        let parsed: IdentityCore = serde_json::from_str(&json).unwrap();
+        assert_eq!(parsed.full_name.as_deref(), Some("Alice Doe"));
+        assert_eq!(parsed.date_of_birth, NaiveDate::from_ymd_opt(1990, 4, 18));
+    }
+
+    #[test]
+    fn empty_identity_omits_all_fields() {
+        let id = IdentityCore::default();
+        let json = serde_json::to_string(&id).unwrap();
+        assert_eq!(json, "{}");
+    }
+}