Fix duplicate Temporal import error in @fedify/sqlite

Remove direct import of Temporal from @js-temporal/polyfill in kv.ts
since tsdown already injects the polyfill via outputOptions.intro.
This prevents "Identifier 'Temporal' has already been declared" error
on Node.js and Bun.

Closes https://github.com/fedify-dev/fedify/issues/487



Co-Authored-By: Claude <noreply@anthropic.com>