This PR is a follow-up to ea1473e532. When we initially added the experimental feature for automatically adding `[grid]` to images, we add the [grid] surrounding images after all the uploads have been completed.
This can lead to confusion when `[grid]` is delayed to be added in the composer, as users may try to add grid manually leading to breakage. This also leads to issues with Discourse AI's automatic image caption feature.
**In this PR**: we simply move the logic to be added when the images are uploaded and processing. This way, `[grid]` surrounding images is added immediately. We also apply a fix for an edge-case to prevent images from being wrapped in `[grid]` when they are already inside `[grid]` tags.
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