chore: bump version to 0.1.0

[aoirint]

Warning

This pull request was created with assistance from LLMs.

Summary

• Bump VERSION from 0.0.0 to 0.1.0.
• Move the prepared changelog entries from Unreleased into
  v0.1.0 - 2026-05-18 UTC.
• Keep the release PR based on main after docs: add changelog #89 was merged.

Related Issues

None

Notes for reviewers

Merging this into main should make the build workflow treat the push as the
first stable SemVer release because v0.1.0 does not currently exist.

AI disclosure

LLM assistance was used to verify the release-mode logic, resolve the stacked
PR after #89 merged, and prepare the changelog release section.

Testing

Automated checks

• Release-mode shell logic from .github/workflows/build.yml:
  tag_exists=false, version=0.1.0, tag=v0.1.0, release_mode=latest
• git diff --check origin/main...HEAD

AI-assisted inspections

Request: Confirm the release PR updates only VERSION and the changelog release
section.

AI-assisted result: Confirmed the PR diff against main changes only
VERSION and CHANGELOG.md, with the changelog material moved from
Unreleased into v0.1.0.