chore: support Node 24

[mashbean]

Summary

• publish the next 0.3.x compatibility release as @matters/matters-editor@0.3.2
• relax engines.node to the transition-safe range >=18.19 <25.0.0
• run PR CI against both Node 18.19 and Node 24
• update publish workflow to Node 24 and remove obsolete npm unsafe-perm

Validation

• npm ci
• npm run lint
• npm run test (4 files / 71 tests)
• npm run build
• packed dist package installed with npm install --engine-strict on Node 24 and @matters/matters-editor/transformers ran html2md

Notes

This keeps the code and dependency graph unchanged. It avoids jumping to the registry's 1.0.3 artifact, which is not tagged as latest and has a different dependency shape.

[mashbean]

Downstream preflight with a locally packed @matters/matters-editor@0.3.2 tarball:

• matters-web: npm install --dry-run --engine-strict <tarball> completed. Since web already consumes 0.3.1, this should be a package metadata/version-only move after publish.
• matters-server: npm install --dry-run --engine-strict <tarball> completed, but server currently consumes 0.3.0-alpha.4; moving to 0.3.2 also moves editor-related Tiptap/ProseMirror dependencies forward. Server should run transformer and mutation smoke checks when it consumes the published package.

Recommended server smoke scope after publish: html2md, md2html, normalizeArticleHTML, normalizeCommentHTML, normalizeMomentHTML, plus publish/edit/draft/comment mutation paths.