docs(repo): add Cursor Cloud specific instructions to AGENTS.md

[Gsbreddy]

Summary

Adds a ## Cursor Cloud specific instructions section to AGENTS.md with non-obvious caveats for future Cloud Agent sessions.

Why

Future Cursor Cloud agents need to know how to run lint/tests/build/serve without re-discovering environment-specific gotchas every session (e.g. Playwright requiring FLIGHTDECK_E2E_PYTHON, flightdeck serve needing an initialized workspace).

Changes

• Added service table (CLI, HTTP server, web dev server)
• Added quick-reference commands for lint, test, smoke, web build, and Playwright e2e
• Documented non-obvious caveats:
  • Playwright e2e needs FLIGHTDECK_E2E_PYTHON pointed at the venv Python
  • flightdeck serve requires a flightdeck.yaml workspace
  • PostgreSQL tests are auto-skipped without env var
  • Static bundle is committed and must be rebuilt after web/ changes

Validation

• uv sync --frozen --extra dev
• uv run python -m ruff check src tests
• uv run python -m pytest
• uv run flightdeck-quickstart-verify
• uv run flightdeck --help
• cd web && npm ci && npm run build && cd .. && git diff --exit-code src/flightdeck/server/static/
• cd web && FLIGHTDECK_E2E_PYTHON=/workspace/.venv/bin/python npm run test:e2e

Schema / Storage Impact

• None

Risk

Docs-only change, no code impact.

Review

• Requested review from maintainers
• PR is small and scoped

Notes

All verification commands pass: 139 pytest tests (83% coverage), 18 Playwright e2e tests, ruff clean, quickstart smoke OK.