fix: Upgrade tsdown in kitchen-sink api to fix dev script (#13105)
## Summary
- Bumps `tsdown` from `0.9.3` to `0.12.0` in the Kitchen Sink `api`
workspace
- Fixes `npm run dev` failing with `FATAL Unknown option --onSuccess` on
fresh `create-turbo -e kitchen-sink` projects
- The `--onSuccess` flag was introduced in tsdown `0.10.2`, but the
template still pinned `0.9.3`
Fixes #13099
## Test plan
- [x] `pnpm install` in `examples/kitchen-sink`
- [x] `pnpm run build` in `examples/kitchen-sink/apps/api` succeeds with
tsdown 0.12.0
- [x] `tsdown --watch --onSuccess` no longer errors with unknown option
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