docs: remove redundant dates from changelog subheaders

[firestar300]

Cleans up the changelog by removing dates from the Added, Changed, and Fixed subheadings, as this information is already provided in the main version headers.

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Note

Low Risk
Low risk documentation-only change that only adjusts CHANGELOG.md formatting and does not affect runtime behavior.

Overview
Removes redundant dates from ### Added/### Changed/### Fixed subheadings in CHANGELOG.md, relying on the version header date instead.

No release notes content changes beyond these heading formatting tweaks.

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