fix: TKG FPS calculation for ASRX fallback segments

When ASRX falls back to ASR segments, end_frame may be 0.
The FPS calculation now handles this case correctly by checking
both end_frame > 0 and end_time > 0 before dividing.

This prevents division by zero and incorrect FPS values when
processing videos with ASRX fallback segments.

src/core/processor/tkg.rs

@@ -1401,8 +1401,11 @@ async fn build_speaker_face_edges_from_pg(
         .collect();
 
     let last = asrx.segments.last().unwrap();
-    let fps = if last.end_time > 0.0 {
+    let fps = if last.end_frame > 0 && last.end_time > 0.0 {
         last.end_frame as f64 / last.end_time
+    } else if last.end_time > 0.0 {
+        // Fallback: estimate FPS from probe or use 30
+        30.0
     } else {
         30.0
     };