Add vace_length field, move end_frame out of VACE settings, revert type coercion

- Moved end_frame to main settings area (i2v field, not VACE)
- Added vace_length (default 49) with computed output display
  showing vace_length + input_a + input_b
- Reverted custom param type coercion (ComfyUI handles conversion)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

utils.py

@@ -38,6 +38,7 @@ DEFAULTS = {
     "frame_to_skip": 81,
     "end_frame": 0,
     "transition": "1-2",
+    "vace_length": 49,
     "vace schedule": 1,
     "input_a_frames": 0,
     "input_b_frames": 0,