Update Changelog

Update CHANGELOG.md with user-facing changes from recent development work.

Input

Primary input: optional start reference — a date (YYYY-MM-DD) or commit hash.

Optional last parameter: -- <additional context>

Interpret $ARGUMENTS as one of:

• <date>
• <commit>
• <date> -- <additional context>
• <commit> -- <additional context>
• -- <additional context>

If no start reference is provided, look at commits since the last changelog update. Use any additional context to influence grouping, emphasis, or release framing.