docs(changelog): reconcile 0.2.0/0.3.0 sections and prepare 0.4.0

[ivanasabi]

Summary

• The release lane keep-a-changelog bump created empty 0.2.0 / 0.3.0 headings (it runs with tag-prefix: ""), while the real content stayed anchored under 0.1.0 (empty Added/Fixed headings left behind).
• Compare links were written without the v prefix, but the published tags are v0.2.0 / v0.3.0 (the Python release lane generates v$version tags).

What changed

• 0.1.0: initial release + Docouture migration (Migrate docs to Docouture #9) + .tool-versions heredoc fix (fix(release): normalize trailing newline in .tool-versions heredoc #11).
• 0.2.0: version alignment only (no functional changes).
• 0.3.0: golden-bytes restore of .tool-versions (chore(ci-governance): restore .tool-versions golden bytes #12).
• Unreleased: restore of code-uv_python-release-core golden bytes (chore(ci-governance): restore release-core workflow to golden bytes #13) -> content for the next release (0.4.0).
• Links now point at the real v* tags.

Verification

• CHANGELOG.md diff is non-empty against main with content under Unreleased -> satisfies the Release Preview changelog gate (code-release_preview.yml:83-a85).

Co-authored-by: Copilot 223556219+Copilot@users.noreply.github.com

[github-actions]

Release Preview

This pull request has the skip-release label and will not create a Python release.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud