Instagram Reels Cover Frame Selection

Title: Instagram Reels: Cover Frame Offset (like TikTok has)

Body:

TikTok already lets you pick a frame from the video as the cover using tiktokSettings.video_cover_timestamp_ms. Would be awesome to have the same thing for Instagram Reels.

Why I want this:

• Quick way to pick a good frame without making a separate image

• Useful when I don't have time to design a custom thumbnail

Suggested API Parameter:

json

{  "instagramSettings": {  "cover_timestamp_ms": 3000  } }

Or in platformSpecificData:

json

{  "platforms": [{  "platform": "instagram",  "platformSpecificData": {  "cover_timestamp_ms": 3000  }  }] }

Note: Instagram's API has thumb_offset for Reels, so this should map pretty cleanly.