Apple targets now support configurable attributes with select()

Attributes marked configurable = True in the Apple prelude now accept a TOML select shape that resolves at analysis time based on the target’s platform, sdk_variant, architecture, and mac_catalyst token. Composite keys such as ios:simulator use longest-match wins, with a required default fallback. The analyzer rejects select() on non-configurable attributes and on attributes that select on architecture during multi-arch builds, producing clear errors instead of silently incorrect values.