Types haven't been bundled by microbundle

Microbundle ignores `*.ts` files if they contain only types. Example of the file: https://github.com/XaveScor/signal-components/blob/dff96fd7151db5aae7421059836794a7880c2649/src/types.ts.

### Reproduction:
```
git clone https://github.com/XaveScor/signal-components
git checkout tags/v0.11.0
pnpm install
pnpm build
```

### Expected Result:
`types.d.ts` is included in the `./dist` directory.

### Actual Result:
`types.d.ts` does not exist. Types are broken because we have `./types` imports, but the file is missing.

Start with the linked signal-components example at src/types.ts and reproduce the issue by checking out tag v0.11.0, running pnpm install, and then pnpm build. Inspect the generated ./dist output and verify that types.d.ts is present and that ./types imports resolve; compare the result with the open linked pull request.

Written by the indexing model from the issue text.