[codex] Prevent stale xPoster image markers

[aa755]

PR created and submitted by codex

What changed

This makes Article imports fail-safe when X's async media upload flow races with xPoster's marker cleanup.

• Waits for any uploaded body images that still lack media IDs to settle before final cleanup.
• Repeatedly removes xPoster marker tokens until the live Draft.js editor is stably marker-free.
• Tracks remaining marker count in the import summary.
• Throws a clear "Do not publish" error if any __XPOSTER_... marker survives cleanup.

Why

A real published Article ended up with an image marker such as __XPOSTER_f4m2b_IMAGE_1__ visible above an uploaded image. The likely interleaving is that xPoster removed a marker, then X applied a later media-upload state update from an older editor snapshot that still contained that marker. The image upload succeeded, but the temporary marker came back.

Validation

• npm run check passed.
• git diff --check passed.
• npm test currently fails on upstream main before reaching this change: shared.normalizeAiCoverSettings is not a function in scripts/smoke-test.js.