ci: remove the repository changelog subsystem

[DecisionNerd]

Problem

GraphForge maintains a large duplicated changelog subsystem across the repository root, published docs, release-note extraction, scheduled release tracking, version bumping, publication preflight, PR guidance, and CI. It has already stopped publication without proving package correctness and now adds ceremony and divergence risk.

Objective

Remove the GraphForge changelog completely as a maintained artifact and as a CI/publication requirement. Release communication should use GitHub Release notes and immutable release metadata instead.

Requirements

• Delete the root and docs-mirror changelog files.
• Remove changelog extraction, mirroring, scheduled tracking, and CI tests/checks.
• Remove the publication-workflow changelog waiver and every changelog preflight condition.
• Remove changelog behavior from version bumping and release automation.
• Remove changelog navigation, docs-site sync, PR-template requirements, Make targets, and current contributor/operator instructions.
• Replace required release-note steps with GitHub-generated or explicitly supplied GitHub Release notes where a release still needs prose.
• Preserve package/version/candidate/checksum/completeness/registry verification and every other release-safety assertion.
• Do not edit generated third-party notices whose changelog text describes an upstream dependency path.

Acceptance criteria

• CHANGELOG.md and docs/reference/changelog.md no longer exist.
• No CI, release, publication, scheduled, Make, or test path reads, compares, writes, or requires a changelog.
• The publication workflow has no changelog waiver or changelog-derived release gate.
• Current docs and templates no longer instruct contributors or operators to update/read a changelog.
• Release notes, when needed, come from GitHub Release metadata rather than a repository mirror.
• Existing package integrity, version-unity, artifact-completeness, credential-isolation, and registry-truth checks remain unchanged.
• Focused tests and normal exact-head CI pass.

Non-goals

• Changing package versions, tags, registry contents, or immutable v0.5.0 records.
• Publishing packages or running a release-certification cascade.
• Rewriting generated third-party legal notices.

[coderabbitai]

🔗 Related PRs

#235 - feat(cli): add Python and Node lifecycle launchers [open]
#282 - fix(release): resume immutable v0.5.0 publication [merged]
#289 - fix(release): amend unpublished main npm artifact [merged]
#297 - docs(release): require one shared product version [merged]
#305 - feat(release): orchestrate resumable publication [open]

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