docs: add changelog baseline

[nike-beep]

Summary

• add CHANGELOG.md with an initial 0.1.0 OSS baseline for the current CLI, runtime, core, host SDK, takeover flow, and experimental FinOps surfaces
• keep the diff inside the capsule boundary by touching CHANGELOG.md only
• avoid stale fixed-coverage or standalone-bundle claims in the changelog entry

Verification

• git diff --check
• attempted pnpm exec vitest run --coverage --coverage.reporter=text-summary --coverage.reporter=json-summary --coverage.exclude='**/dist/**' from the repo root; the current baseline still has unrelated Windows/environment-sensitive test failures

Test Coverage

• Docs-only change; changed-file coverage is not applicable because no executable files changed in this diff
• Full coverage run is currently red on the base repository for unrelated runtime/CLI tests, so this PR does not introduce the failure state