Introduces DataManagerEnvironmentKey + EnvironmentValues.dataManager so
SwiftUI views can resolve DataManagerObservable via @Environment, mirroring
Compose's LocalDataManager ambient on the Kotlin side.
No view migrations yet — views continue to read DataManagerObservable.shared
directly. The actual screen-level substitution (fake DataManager for
parity-gallery / tests / previews) lands in P1 when ViewModels gain an
optional init param that accepts the environment-resolved observable. For
this commit we only need the key so P1 can wire against it.
Note: the iosSimulator Kotlin compile is broken at baseline (bb4cbd5)
with pre-existing "Unresolved reference 'testTagsAsResourceId'" errors
across 20+ screen files — Android-only semantics API imported in
commonMain. Swift-parse of the new file succeeds. Verified by checking
out bb4cbd5 and rerunning ./gradlew :composeApp:compileKotlinIosSimulatorArm64.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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