feat: auto-populate key_frame and key_face in TKG face_track nodes

- FacePoint now includes confidence and point_id from Qdrant
- TKG build tracks best face (highest confidence) per trace
- key_frame = frame number of best face, key_face = Qdrant point ID
- Every face trace now has representative frame and face for UI display

src/core/processor/tkg.rs

@@ -19,6 +19,8 @@ struct FacePoint {
     y: f64,
     w: f64,
     h: f64,
+    confidence: f64,
+    point_id: Option<String>,
 }
 
 /// Scroll all face points for a file from Qdrant _faces collection
@@ -118,6 +120,8 @@ fn parse_face_points(points: Vec<serde_json::Value>) -> Vec<FacePoint> {
                 y,
                 w,
                 h,
+                confidence: payload["confidence"].as_f64().unwrap_or(0.5),
+                point_id: p["id"].as_u64().map(|id| id.to_string()),
             })
         })
         .collect();
@@ -1127,6 +1131,9 @@ async fn build_face_track_nodes_from_qdrant(
         sum_w: f64,
         sum_h: f64,
         frames: Vec<(i64, f64, f64, f64, f64)>, // (frame, x, y, w, h)
+        best_frame: i64,
+        best_confidence: f64,
+        best_point_id: Option<String>,
     }
 
     let mut traces: HashMap<i64, TraceAgg> = HashMap::new();
@@ -1140,6 +1147,9 @@ async fn build_face_track_nodes_from_qdrant(
             sum_w: 0.0,
             sum_h: 0.0,
             frames: vec![],
+            best_frame: 0,
+            best_confidence: 0.0,
+            best_point_id: None,
         });
         entry.frame_count += 1;
         entry.start_f = entry.start_f.min(p.frame);
@@ -1149,6 +1159,12 @@ async fn build_face_track_nodes_from_qdrant(
         entry.sum_w += p.w;
         entry.sum_h += p.h;
         entry.frames.push((p.frame, p.x, p.y, p.w, p.h));
+        // Track best face (highest confidence)
+        if p.confidence > entry.best_confidence {
+            entry.best_confidence = p.confidence;
+            entry.best_frame = p.frame;
+            entry.best_point_id = p.point_id.clone();
+        }
     }
 
     let mut count = 0;
@@ -1187,6 +1203,8 @@ async fn build_face_track_nodes_from_qdrant(
             "frame_count": agg.frame_count,
             "start_frame": agg.start_f,
             "end_frame": agg.end_f,
+            "key_frame": agg.best_frame,
+            "key_face": agg.best_point_id.as_deref().unwrap_or(""),
             "avg_bbox": {
                 "x": (agg.sum_x / agg.frame_count as f64).round() as i64,
                 "y": (agg.sum_y / agg.frame_count as f64).round() as i64,