chore(docs): consolidate duplicate ### Added / ### Changed / ### Fixed blocks under Unreleased in CHANGELOG.md #76

Context

CHANGELOG.md's ## Unreleased section has accumulated multiple duplicate ### Added, ### Changed, and ### Fixed subsection headers from merged PRs each adding their own section rather than consolidating into the first block. Keep a Changelog format expects one of each subsection per release — duplicates make the file harder to scan and can break tooling that parses it.

Current state (as of #75 open): at least 3 ### Fixed headers, 3 ### Changed headers, 2 ### Added headers all within one ## Unreleased. Introduced by #55, #65, #71 and others.

Acceptance

• ## Unreleased has exactly one ### Added, one ### Changed, optionally one ### Removed, one ### Fixed — in Keep a Changelog canonical order.
• All existing bullet points preserved under their correct subsection.
• No content loss — just header consolidation + re-sorting bullets into their correct type.

Why not fix now?

Best done during release-cut, when someone's already restructuring ## Unreleased into a named ## [1.0.0] - YYYY-MM-DD section. Doing it mid-Unreleased-accumulation is churn: every subsequent PR will re-fracture the blocks unless we also add CI enforcement, which is its own scope.

Flagged by Copilot on #75.

— Posted by Claude Code on behalf of @EricAndrechek