docs(standard): pin the floors with builds allowed, then install them wheel-only

[lesnik512]

CI6 now prescribes how the floors job installs: two uv commands, the first pinning each declared floor with builds allowed and the second installing those pins with builds disabled.

Why

Wheel-only on its own doesn't fail on a floor that has no wheel. --no-build or --only-binary makes that version ineligible, and --resolution lowest-direct then climbs to the lowest version that has a wheel, so the job passes on a version the repo never declared. compose2pod's PyYAML>=6 resolved 6.0.1 and 6.0.2 on 3.12 and 3.13 while its gate stayed green (compose2pod#135). uv treats this as intended (astral-sh/uv#16186) and has no option that turns the climb into an error.

Resolving first with builds allowed pins the declared floor itself, and the wheel-only install then fails on it. compose2pod#139 piloted this. A throwaway PR that planted PyYAML>=6 on 3.12 failed only its floors (3.12) leg, at the install step.

Consequences for the repos

• -r pyproject.toml installs the dependencies but not the project, so --no-install-project and the carve-out for building the project both go away. The tests import the project from the checkout, as before.
• The dev group installs at newest (--group dev). Only the project's own dependencies are pinned, so dev dependencies no longer need floors to get a usable test harness.
• Larger projects work the same way: sunpy, jwst, napari, scikit-image and scikit-learn test exact minimum pins rather than a lowest resolution.

The sweep that applies this to the 20 repos installing with uv sync --no-install-project follows. lite-bootstrap installs per-target extras and needs its own change.