docs(changelog): merge the duplicate Fixed heading under Unreleased

[datlechin]

[Unreleased] carries two ### Fixed headings. CLAUDE.md calls that out by name: "Each section appears at most once per version, in that order; a second ### Security under one version is a defect, not a second topic."

The second one arrived with the editor tab work, after a ### Changed that was itself appended below the first ### Fixed rather than above it.

This merges the two and puts the sections back in the canonical order, Added then Changed then Fixed. Entry text is untouched and no entry moves relative to the others inside its own section.

Found while working on #2427, where it was noticed rather than fixed, because restructuring [Unreleased] conflicts with every branch that has an entry in flight. It is here on its own so it can go in quickly and the conflicts stay small.

Verification

• 21 entries under [Unreleased] before, 21 after.
• 119 ## [ release headings before and after, so nothing folded a shipped version into [Unreleased].
• The diff is 4 insertions and 7 deletions: the ### Changed block moves up, and the second ### Fixed heading goes.

https://claude.ai/code/session_01KsqHrFwJxUW6eWozYjT8JZ

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