chore: release 0.2.0

[OndrejDrapalik]

Summary

Cuts 0.2.0 from what #20 and #21 landed. feat in a pre-1.0 project bumps the minor, which is the
rule this repo's own history sets — 0.1.0 carried feat! entries as a minor.

Both version files move together (package.json, herdr-plugin.toml), because CI's version-check
job and the release workflow each assert independently that they match the tag.

The changelog needed surgery, not just a rename

#20's 26 changelog lines were written against ## [Unreleased]. v0.1.0 renamed that heading, but
the hunk's context still matched — so the merge landed those bullets inside the published [0.1.0]
section, cleanly and silently, quietly rewriting what a shipped release claims to contain. Nothing
catches this: git reports a clean merge and version-check only compares the two version files.

So this PR relocates them into the new [0.2.0] section where they belong, leaves [0.1.0] reading
exactly as it did when it shipped, and adds a ### Fixed bullet for #21, which merged with no
changelog entry of its own.

It also leaves an empty ## [Unreleased] heading behind. That is the actual fix for the trap above:
without it, the next contributor adding a bullet to "the top of the changelog" files it into a
published release again.

Verification before tagging

• scripts/changelog-notes.sh 0.2.0 extracts 34 non-empty lines — an empty section hard-fails the
  release workflow after it has installed a cross-compile toolchain and built three binaries, with
  the tag already public
• npm test green locally; both version files read 0.2.0; v0.2.0 is free
• [0.1.0] verified to no longer contain feat: the board names each box's template and region #20's bullets

Test plan

• Full suite green locally
• Release preflight clean apart from this branch not yet being on main
• v0.2.0 tag publishes with all three dashboard binaries attached