next 16.3 type-checks the whole tsconfig program during the build. That
reaches the unit tests under src/**/__tests__, their fixtures under
tests/, the Playwright config and the e2e tree, none of which is in the
image build context — .dockerignore leaves tests/ and e2e/ out on
purpose — so the image build stopped at "Cannot find module
'../../tests/fixtures/...'" on both architectures.
The build now reads tsconfig.build.json, which extends the main tsconfig
and excludes the test tree and the test-runner configs. `pnpm typecheck`
keeps using tsconfig.json and still covers the full program; the change
narrows only what `next build` compiles, which was already the case on
16.2 by omission. Verified by building with tests/ and e2e/ moved away.
