feat(tkg): add Qdrant retry logic with exponential backoff

- scroll_face_points now retries up to 3 times on failure
- Exponential backoff: 1s, 2s, 4s between attempts
- Logs retry attempts for debugging
- Prevents silent failures when Qdrant is temporarily unavailable

src/core/processor/tkg.rs

@@ -34,18 +34,46 @@ async fn scroll_face_points(file_uuid: &str) -> Vec<FacePoint> {
         ]
     });
 
-    let points = match qdrant.scroll_all_points("_faces", filter, 500).await {
-        Ok(pts) => pts,
-        Err(e) => {
-            tracing::error!(
-                "[TKG-Qdrant] Failed to scroll _faces for {}: {}",
-                file_uuid,
-                e
-            );
-            return vec![];
+    // Retry with exponential backoff (3 attempts)
+    let mut last_err = None;
+    for attempt in 1..=3 {
+        match qdrant.scroll_all_points("_faces", filter.clone(), 500).await {
+            Ok(pts) => {
+                if attempt > 1 {
+                    tracing::info!(
+                        "[TKG-Qdrant] scroll succeeded on attempt {} for {}",
+                        attempt,
+                        file_uuid
+                    );
+                }
+                return parse_face_points(pts);
+            }
+            Err(e) => {
+                last_err = Some(e);
+                if attempt < 3 {
+                    let delay_ms = 1000 * 2_u64.pow(attempt as u32 - 1); // 1s, 2s, 4s
+                    tracing::warn!(
+                        "[TKG-Qdrant] scroll attempt {} failed for {}: {} (retrying in {}ms)",
+                        attempt,
+                        file_uuid,
+                        last_err.as_ref().unwrap(),
+                        delay_ms
+                    );
+                    tokio::time::sleep(std::time::Duration::from_millis(delay_ms)).await;
+                }
+            }
         }
-    };
+    }
 
+    tracing::error!(
+        "[TKG-Qdrant] Failed to scroll _faces for {} after 3 attempts",
+        file_uuid
+    );
+    vec![]
+}
+
+/// Parse FacePoint structs from Qdrant response
+fn parse_face_points(points: Vec<serde_json::Value>) -> Vec<FacePoint> {
     points
         .iter()
         .filter_map(|p| {