chore: prep v0.5.5 release

docs/RELEASING.md

@@ -0,0 +1,21 @@
+<!-- read_when: cutting a tagged release or debugging release prep -->
+
+# Releasing
+
+1. Confirm `main` is green: `gh run list --workflow CI --limit 5`.
+2. Bump `package.json` to the release version.
+3. Build release metadata before tagging:
+   `bun run changelog:build --version <version>`
+4. Review `CHANGELOG.md`.
+5. Run release gate locally:
+   `bun run changelog:check --version <version>`
+   `bun run test:fast`
+   `bun run typecheck`
+6. Commit release prep.
+7. Tag the commit: `git tag v<version>`.
+8. Push commit + tag.
+
+Notes:
+
+- `changelog:check` now rejects tag/package version mismatches.
+- Do not tag while `changes/*.md` fragments still exist.