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)

Cargo.lock

@@ -636,6 +636,8 @@ dependencies = [
  "compression-core",
  "flate2",
  "memchr",
+ "zstd",
+ "zstd-safe",
 ]
 
 [[package]]