docs: add CHANGELOG entry for v0.2.1

Summarizes the Copilot SDK v0.3.0 upgrade that fixes bash tool
permissions, the interactive mode fix, and the working directory
support addition.

chore: add CHANGELOG.md for v0.2.0 release

Merge pull request #1 from alxayo/copilot/fix-github-actions-workflow

fix: escape Scoop autoupdate `$version` placeholder in release workflow heredoc