fix: keep astro check out of dist after a local build

[eseidel]

A second npm run build in the same checkout fails: astro check type-checks the bundled JavaScript in dist/ left by the first build and aborts. CI never sees it because it builds from a clean checkout, so it only bites locally, and the workaround is deleting dist/ before every build.

The cause is tsconfig.json's exclude. Astro's base tsconfig excludes dist, but setting exclude here replaces that list instead of adding to it, so dist was no longer excluded once functions was. This puts dist back next to functions.

Checked by building with a stale dist/ present: astro check reports 0 errors and the build completes.

[eseidel]

lgtm