fix: publish root TypeScript declarations for CommonJS consumers

[bcornish1797]

@algora-pbc /claim #135

This keeps the package CommonJS-first and avoids a build step, while making published typings usable from TypeScript NodeNext consumers.

What changed:

• add a root index.d.ts so import seeli from "seeli" resolves declarations from the package entrypoint
• publish that file via files and point package.json#types at it
• align existing declaration signatures with runtime behavior, especially run() paths that can return undefined

Verification:

• npm test
• npm run lint (warnings only from generated .tap report files, no errors)
• packed-package verification in a fresh consumer project:
  • npx tsc --pretty false with module=NodeNext
  • require("seeli")
  • import seeli from "seeli"

This follows the maintainer guidance from #135: CommonJS-first, no TypeScript build step, and focused on publishable type definitions rather than rewriting the runtime to TS/ESM.

[esatterwhite]

Thanks @bcornish1797 I'll try to get to this in the next day or so

[esatterwhite]

@bcornish1797 Can you rerun npm run lint:fix and recommit? That should fix the codacy quality issues

[bcornish1797]

Done — I ran npm run lint:fix, committed the formatting-only change, and pushed it to the PR branch in cb3e363.\n\nI also re-ran lint and the test suite locally; both pass, so Codacy should have what it needs now.