feat: progressive multi-round face matching + pending person API

- Identity agent: per-face max matching, multi-round with derived
  seeds from high-confidence faces, angle diversity filter (cosine sim < 0.90)
- Pending person API: POST /file/:file_uuid/pending-person
  + GET /file/:file_uuid/pending-persons with status=pending, source=manual
- Update API docs (07_identity.md)

src/core/person_identity.rs

@@ -69,7 +69,8 @@ pub struct IdentityBinding {
 #[derive(Debug, Clone, Deserialize, Serialize)]
 pub struct BindIdentityRequest {
     pub file_uuid: String,
-    pub face_id: String,
+    pub face_id: Option<String>,
+    pub id: Option<i64>,
 }
 
 #[derive(Debug, Clone, Deserialize, Serialize)]
@@ -81,7 +82,8 @@ pub struct BindIdentityTraceRequest {
 #[derive(Debug, Clone, Deserialize, Serialize)]
 pub struct UnbindIdentityRequest {
     pub file_uuid: String,
-    pub face_id: String,
+    pub face_id: Option<String>,
+    pub id: Option<i64>,
 }
 
 #[derive(Debug, Clone, Deserialize, Serialize)]