Route configured prebuilt profiles through bootstrap and wheel downloads #1208

Summary
Make pypi-prebuilt and hook-prebuilt follow the prebuilt wheel path, while using the selected source resolver to download a wheel when one is needed.

Context
Both profiles declare resolves_prebuilt_wheel=True. Today, PackageBuildInfo.pre_built only reads the legacy variant setting, so bootstrap treats a configured prebuilt profile as a source build. The existing prebuilt paths also call wheels.download_wheel() directly. Changing only the prebuilt decision would still bypass hook-prebuilt’s download hook.
Bootstrap and later build commands run separately, so both must honor the configured profile. Legacy pre_built packages must keep their current behavior.

Acceptance Criteria

• When source: is configured, the prebuilt decision uses source_resolver.resolves_prebuilt_wheel. Without source:, it uses the existing legacy setting.
• pypi-prebuilt and hook-prebuilt skip source preparation and source-build phases. The dependency graph and build order record them as prebuilt.
• When either configured profile needs a fresh wheel, its resolver’s download() contract supplies the wheel path. An installed hook-prebuilt download hook runs; the profile’s existing default runs when that hook is absent.
• Bootstrap and commands that fetch wheels from a build order honor that download contract. Intentional reuse of an existing wheel remains possible.
• A result with a kind other than prebuilt_wheel, or a download-hook failure, produces a clear error rather than falling back to a different downloader.
• Tests cover both configured profiles, hook present and absent, build-order replay, and unchanged legacy prebuilt behavior.