chore: improve docflow github action workflow

[Zih0]

Summary

• Set up Changesets for versioning/publishing and migrate the Release workflow to changesets/action.
• Add a dedicated CI workflow to run lint / build / typecheck / test on PRs and main.
• Split out docs deployment into its own workflow (Vercel deploy from docs/).
• Update root scripts to run workspace commands only for packages/* (exclude docs): lint, typecheck, build, test.
• Stabilize test workspaces by setting packageManager in generated package.json to avoid Corepack warnings.

[vercel]

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Project	Deployment	Review	Updated (UTC)
docflow-docs	Ready	Preview, Comment	Jan 19, 2026 1:17pm