Cut the 0.3.0 changelog

[sehkone]

Context

Everything 0.3.0 carries has landed and sits under ## Unreleased in CHANGELOG.md, scoped across all four areas: the ClumL company mark replacing a product logo (#38), and the build provenance line on PDF covers (#33).

release.yml extracts release notes by grepping ^## \[$VERSION\]. A tag pushed against a bare ## Unreleased produces Release for version 0.3.0 as the entire release body — and that is what the Slack subscription posts. Cutting the heading is a prerequisite for tagging, not a tidy-up.

0.3.0 rather than 1.0.0, and MINOR rather than MAJOR, both follow the policy already in the README: brand.svg changes what it depicts, which is breaking for anything rendering it on a light background, and below 1.0.0 a breaking change bumps MINOR. The project stays on 0.x until a consumer has actually adopted the contract, which is the next piece of work.

Scope

Promote ## Unreleased in CHANGELOG.md to ## [0.3.0] with the release date, and add the matching link reference beside the existing [0.2.0] and [0.1.0] ones.

The entries are already written and scoped by area. Do not rewrite them.

Acceptance criteria

• CHANGELOG.md has a ## [0.3.0] heading that release.yml can extract, and no empty ## Unreleased section is left behind.
• A [0.3.0] link reference exists alongside [0.2.0] and [0.1.0].
• Running release.yml's extraction logic against the new heading yields the scoped entries rather than the one-line fallback.
• scripts/check-release-surface.sh accepts the change: the release surface differs from 0.2.0, so the guard has something to release.
• markdownlint-cli2 passes and the file stays within the 80-column limit MD013 enforces.

Constraints

• Do not edit the existing Unreleased entries.
• Do not touch README.md. The 0.x rule it needed was added for 0.2.0 and still applies.
• Do not create the tag. Tagging is a separate manual step.

[sehkone]

Scope grew: the file had drifted from the format bootroot and agentcoop use, so aligning it is a prerequisite for cutting anything in it.

Three deviations, all introduced when the area-scoped convention was adopted:

	house format	docs-theme before
header	Keep a Changelog + SemVer blurb	a note explaining the local convention
sections	### Added / Changed / Fixed / Removed	### manual / api-reference / shared / scripts
link refs	compare/<prev>...<ver>, plus [Unreleased]	tree/<ver>, no [Unreleased]

The area grouping also duplicated itself: nine bullets under 0.2.0 appeared verbatim under both manual and api-reference, because a change affecting both templates had to be written twice. That is most of why the rewrite is 148 lines shorter than what it replaces.

0.2.0's published release notes are unaffected — they were extracted at tag time and live on the release page.