fix: strip data URI prefix before sending image to video API

The Freepik video generation API expects raw base64, not a data URI
(data:image/jpeg;base64,...). Strip the prefix in VideoAPI.generate
before building the payload.

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

freepik_cli/api/videos.py

@@ -32,6 +32,10 @@ class VideoAPI:
         seed: Optional[int] = None,
     ) -> str:
         """Submit an image-to-video task. Returns task_id."""
+        # Video API expects raw base64, not a data URI
+        if ";base64," in image_b64:
+            image_b64 = image_b64.split(";base64,", 1)[1]
+
         image_field = VIDEO_IMAGE_FIELDS[model]
 
         # kling-elements uses an array; all others use a scalar