chore: use tsdown

[gabrielmfern]

tsup is not actively maintained anymore and recommends that tsdown is used instead, so this migrates to tsdown which React Email has already done a while ago

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Summary by cubic

Migrated the build system from tsup to tsdown and updated package exports to use module-aware types (.d.mts/.d.cts) and CJS output (.cjs) for better ESM/CJS interop.

• Refactors

  • Switched build script to tsdown (esm, cjs, dts).
  • Updated exports: types to .d.mts/.d.cts and CJS default to index.cjs.

• Dependencies

  • Removed tsup; added tsdown@0.16.5.
  • Regenerated pnpm-lock.yaml.

^{Written for commit 348e08b. Summary will update automatically on new commits.}

[socket-security]

Review the following changes in direct dependencies. Learn more about Socket for GitHub.

Diff	Package	Supply Chain Security	Vulnerability	Quality	Maintenance	License
	tsdown@​0.16.5

View full report

[cubic-dev-ai]

2 issues found across 2 files

Prompt for AI agents (all 2 issues)

Understand the root cause of the following 2 issues and fix them.


<file name="package.json">

<violation number="1" location="package.json:27">
The `tsdown` build command is likely misconfigured and will not produce the output files with the extensions (`.mjs`, `.cjs`, `.d.mts`, `.d.cts`) defined in the `package.json` `exports` map, breaking package resolution.</violation>

<violation number="2" location="package.json:71">
tsdown@0.16.5 requires Node &gt;=20.19.0, but this package still advertises support for Node &gt;=18. Under a Node 18 setup (or even Node 20.18) the new build step fails to load tsdown’s native binding, so `pnpm run build`/`prepublishOnly` will break for contributors using the documented engine range.</violation>
</file>

_{Reply to cubic to teach it or ask questions. Re-run a review with @cubic-dev-ai review this PR}