docs: fold Unreleased into the 0.2.0 changelog entry

[psyinf]

The v0.2.0 tag points at 703c3bc (#21), so the release includes everything since v0.1.0. CHANGELOG.md still listed [0.2.0] - 2026-09-15 with only three items, and everything since then under [Unreleased].

• Merges [Unreleased] into [0.2.0], dated 2026-09-21, and puts the earlier 0.2.0 items first.
• Leaves an empty [Unreleased] for the next changes.
• Updates the text DSL front-end item: it said execution was a planned follow-up, and DslFilterGraph now ships in the same release.
• The compare links at the bottom were already correct and are unchanged.

The v0.2.0 release notes link to CHANGELOG.md on main, so they point at the right section once this merges. Docs only.