devex: changelog system

[IMB11]

We really suck at changelogs - we should be documenting everything we do - this will encourage it.

• Introduces a fragment-based changelog system using YAML files in .github/changelog/, with scripts to create and bake them into packages/blog/changelog.ts
• Moves changelog data from @modrinth/utils to @modrinth/blog
• Adds CI workflow to remind PR authors to include a changelog fragment, with automatic comment cleanup when one is added - it's always going to be optional though.
• Adds automatic GitHub release creation with changelog body to the Modrinth App release workflow - will document this in Notion.
• Fragment filenames are now descriptive: <product>-<type>-<hash>.yml

Workflow changes include:

• pnpm changelog <product> "description" — fast path to create a changelog fragment (type inferred from prefix e.g. "Fixed ...", "Added ...")
• pnpm changelog - interactive prompt to create changelog fragments
• pnpm changelog:bake -- --product <name> [--version X.Y.Z] — consumes fragments and inserts entries into changelog.ts
• pnpm changelog:bake -- --product app --version X.Y.Z --extract — outputs the baked body for a version (used by CI)
• pnpm changelog:bake -- --product web is the same as running it for both hosting + platform.

CI changes:

• changelog-check.yml — on PRs, posts a bot comment if no changelog fragment is present; minimizes it as outdated once one is added
• theseus-release.yml — now extracts the app changelog and creates a GitHub release with it

Also did some small improvements to the changelog.vue page

• Deploy workflow switches from the github actions bot to the Modrinth bot account as I saw some permission issues were happening with github actions bot - can break with PRs being moved from draft -> ready quite easily

[modrinth-bot]

Note

No changelog fragment was found for this pull request. If this PR includes user-facing changes, create one:

pnpm changelog <platform|app|hosting> "description"

[github-actions]

Frontend previews

Last deployed commit is e97b09900a3b957fb5ad5c871e288de85699724a

Environment	URL
staging	https://git-e97b0990-frontend-staging.modrinth.workers.dev
production	https://git-e97b0990-frontend.modrinth.workers.dev