fix: TKG rebuild type mismatch and face_track nodes

- Fix trace_id type mismatch (INT4 vs i64) with explicit ::bigint cast
- Change build_face_track_nodes to use from_pg version
- Add skin_tone_trace_nodes to API response
- Add #[derive(Serialize)] to TkgResult
- Fix Unicode panic in text label truncation
- Add push_existing_embeddings.py script

src/core/processor/tkg.rs

@@ -458,6 +458,7 @@ struct FaceDetectionRow {
 
 // ── Public API ────────────────────────────────────────────────────
 
+#[derive(Debug, Serialize)]
 pub struct TkgResult {
     pub face_track_nodes: usize,
     pub gaze_track_nodes: usize,
@@ -554,7 +555,7 @@ async fn build_face_track_nodes(
     file_uuid: &str,
     pose_data: &[FacePose],
 ) -> Result<usize> {
-    build_face_track_nodes_from_face_json(pool, file_uuid, pose_data).await
+    build_face_track_nodes_from_pg(pool, file_uuid, pose_data).await
 }
 
 async fn build_face_track_nodes_from_pg(
@@ -2228,8 +2229,8 @@ async fn build_text_region_nodes(pool: &PgPool, file_uuid: &str) -> Result<usize
         &rows
     {
         let external_id = format!("text_{}", chunk_id);
-        let label = if text.len() > 50 {
-            format!("Text: {}...", &text[..47])
+        let label = if text.chars().count() > 50 {
+            format!("Text: {}...", text.chars().take(47).collect::<String>())
         } else {
             format!("Text: {}", text)
         };
@@ -2587,7 +2588,7 @@ async fn build_skin_tone_trace_nodes(
     let mut count = 0;
 
     let rows: Vec<(i64, i64)> = sqlx::query_as(&format!(
-        "SELECT trace_id, COUNT(*) \
+        "SELECT trace_id::bigint, COUNT(*)::bigint \
          FROM {} \
          WHERE file_uuid = $1 AND trace_id IS NOT NULL \
          GROUP BY trace_id",