fix: bugs and code quality in embeddings, jobs, diversity, config

- embeddings: initialize ctx_id=-1 before try block so the except
  handler cannot NameError; move insightface_home out of try for the
  same reason
- embeddings: replace contextlib.redirect_stdout/stderr (Python-level
  only) with fd-level dup2 suppression — actually silences C extension
  noise from InsightFace during model loading
- jobs: fix frigate_count==0 falling through `or` chain; use explicit
  `is not None` check so a real zero is not treated as missing data
- diversity: thread person_id through select_diverse_assets →
  _select_by_embedding → _get_face_bbox / _get_face_confidence /
  _crop_face_from_thumbnail so group-photo assets embed the target
  person's face rather than whichever person is listed first
- config: replace type() hack for ConfigManager with a proper class

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

winnow/config.py

@@ -161,7 +161,12 @@ class _ConfigAccessor:
 
 
 Config = _ConfigAccessor()
-ConfigManager = type("ConfigManager", (), {"get": staticmethod(lambda: _Config())})
+
+
+class ConfigManager:
+    @staticmethod
+    def get() -> _Config:
+        return _Config()
 
 
 def get_headers() -> dict[str, str]: