Speed up Windows app installs and foundation checks

[ymichael]

Human comments

What was wrong

Windows app test shards installed all 2,320 workspace dependencies, including unrelated mobile and desktop packages. Foundation checks also forced every lint, typecheck, and test task to rerun while every other Windows test job could reuse Windows-only cached results.

What changed

App test shards install the root tools and the transitive dependencies of @bb/app and @bb/db; the database is required by the shared native-module check. Foundation checks now restore and save Windows-only Turbo results with the same 256 MB limit and used-entry pruning as the other Windows test jobs. Test commands and cross-platform coverage are retained. Updated the CI performance and Windows documentation.

How you verified

• Windows benchmark 37539104123 compares two full installs (66s, 72s) and two scoped installs (36s, 44s), each followed by the same forced app-test shard. All four benchmark jobs passed.
• pnpm exec turbo run test --filter=@bb/scripts -- test/ci-workflow.test.ts: passed both tests and all six Turbo tasks.
• Actionlint, formatting, and git diff --check passed.
• Full PR CI run 37539619987: all 33 active jobs passed. Windows app installs took 35–45 seconds; those jobs took 81–106 seconds after runner startup with cached tests. This improves setup time; it does not claim the complete cross-platform workflow meets the requested two-minute target.

AGENT GENERATED