[iamfatness]

Fixes #1203.

Windows Zoom camera ISOs use the resolution applied at meeting join as their fixed MP4 size. Incoming frames are fit to that size with their aspect ratio preserved. Matching frames take the existing I420-to-NV12 path, retaining the detail Zoom delivers when it ramps up. Writer preparation uses the fixed size, and encoder admission accounts for the larger of Program and the known ISO sizes.

Validation

• The Windows Release regression recorded 360p → native-size → 360p using the real Media Foundation writer with synthetic frames. It checked all nine decoded frames in each of the 1080p, 720p, and 360p files. The 1080p and 720p segments retained the original two-pixel luma pattern.
• The same test with the previous writer failed at the 1080p case because it produced a 640×360 track. Restoring the fix and rebuilding passed again.
• All 13 focused Windows tests passed, including source selection, Zoom join preferences, writer preparation, eight concurrent ISO writers, and frame scaling.