Back to Search-quality baseline: cross-source canonical (Phase 1.2, v1.2.0 candidate)

For 19 queries where the expected top-1 source was apple-docs (weight 3.0), the actual top-1 was always apple-docs:

`concurrency`, `actor`, `Hashable`, `Sendable`, `Result Builders`, `Property Wrappers`, `async await`, `Generics`, `Observation`, `Optional`, `Protocol`, `Closure`, `Color`, `Navigation`, `Button`, `Typography`, `Materials`, `Privacy`, `Widget`.

The source-weight machinery is doing exactly the work the design intends for the apple-docs-canonical case.