[QTI] Resized images in legacy exercise questions publish without GIF animation or photo orientation #6213

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Target branch: unstable

Observed behavior

When a legacy exercise question has a sized image (![alt](… =WxH)), publishing ships the re-encoded copy from resize_image. The rich text editor writes a size for every image it loads, so this also happens to images the author never resized. Both the Perseus zip and the QTI package show it:

• An animated GIF (3 frames, 120x90) publishes as a single-frame GIF.
• A JPEG with EXIF orientation 6 (stored 400x300, displayed 300x400) publishes as its 400x300 pixels stretched to 300x400, with the EXIF removed. It shows sideways and squashed.

Errors and logs

None. resize_image succeeds and logs nothing.

Expected behavior

A sized image publishes at its authored size, with GIF animation and photo orientation kept.

User-facing consequences

Learners see a still frame where the author used an animation. Phone photos, such as a picture of a worksheet, appear rotated and distorted.

Steps to reproduce

1. On unstable (1beec6e), add a legacy single-choice question and insert an animated GIF and a portrait phone photo with EXIF orientation 6.
2. Publish the channel.
3. Open the exercise's Perseus zip (images/) or QTI package (items/images/). The GIF has 1 frame, and the JPEG has no EXIF orientation, with its landscape pixels stretched to the portrait size.

Acceptance Criteria

• A sized animated GIF in a legacy question publishes with all its frames in the Perseus zip and the QTI package.
• A sized JPEG with EXIF orientation displays upright and undistorted at its authored size in both archives.
• Publish tests cover both cases.

AI usage

Claude Code found this while reviewing the #6189 branch. It reproduced the bug on unstable by publishing generated test images, and drafted this issue.