insight-chat: code-review polish on get_faces_in_photo

- Drop redundant `use anyhow::Context` inside has_any_faces (already
  imported at the module level).
- Drop dead `.unwrap_or("?")` on bound faces — the vec is filtered to
  is_some() so the fallback can never fire.
- Reorder the face_dao constructor param + initializer to match the
  struct declaration (between tag_dao and knowledge_dao). Update both
  state.rs call sites and populate_knowledge.rs to match.
- Hold face_dao lock once across the library-resolver loop instead of
  reacquiring per iteration.

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

src/faces.rs

@@ -1437,7 +1437,6 @@ impl FaceDao for SqliteFaceDao {
     }
 
     fn has_any_faces(&mut self, ctx: &opentelemetry::Context) -> anyhow::Result<bool> {
-        use anyhow::Context;
         let mut conn = self.connection.lock().expect("face dao lock");
         trace_db_call(ctx, "query", "has_any_faces", |_span| {
             face_detections::table