docs(agents): add Cursor Cloud setup and run caveats

[Jwatzkin77]

Summary

Sets up the development environment for the B2B Buyer Portal in Cursor Cloud and documents the non-obvious caveats discovered during setup. No application code changed — only AGENTS.md gains a ## Cursor Cloud specific instructions section.

What was verified (all from apps/storefront/)

Workflow	Command	Result
Lint	yarn lint	✅ pass (depcruise + eslint + knip)
Test	CIRCLECI=true yarn test --run	✅ 1303 tests pass
Build	yarn build	✅ builds dist/
Run	yarn dev	✅ serves on http://localhost:3001

Key caveats documented in AGENTS.md

• Node/PATH: repo needs Node >=22.16.0, but the VM default node (22.14.x) shadows nvm on PATH. Prepend the nvm 22.16 bin dir before running yarn.
• Tests: per-test timeout is 5s unless CIRCLECI=true (40s). This VM is slow enough that heavier suites (e.g. QuickOrder) can spuriously time out at 5s; run with CIRCLECI=true.
• Running the app: it's an injectable widget, not a standalone site. yarn dev serves a mock storefront harness; the portal only mounts on a #/ hash and needs window.B3 config + reachable B2B/BC backends. Offline core-functionality verification is via the Vitest + MSW suite.

Hello-world (offline core functionality)

Ran the real Login page integration suite — 30 tests including the full login flow (exchanges the customer JWT for a B2B token, stores both, and navigates on success).