Adding support for iOS using KMP

[zurche]

KMP: shared core + Compose UI, iOS app bootstrap, and persistence updates

Summary

This PR migrates the calculator core and UI to a shared KMP module, adds an iOS app wrapper using Compose Multiplatform, and updates Android wiring to consume the shared store. It also replaces the JVM-only engine with a KMP-safe parser, restores Android fonts via androidMain, and documents the iOS setup.

Key changes

• Shared KMP module with engine, models, state/store, and Compose UI.
• Android ViewModel now delegates to shared CalculatorStore.
• iOS app scaffolding (SwiftUI host + CocoaPods integration).
• iOS persistence via NSUserDefaults repository.
• Fonts restored on Android via expect/actual typography.

Architecture (after)

graph TD
  subgraph Shared[KMP shared]
    UI[Compose UI]
    Store[CalculatorStore]
    Engine[CalculatorEngine]
    Repo[HistoryRepository]
  end

  subgraph Android[Android app]
    VM[CalculatorViewModel]
    DS[DataStoreHistoryRepository]
  end

  subgraph iOS[iOS app]
    Swift[SwiftUI Host]
    IOSRepo[IosHistoryRepository]
  end

  Swift --> UI
  VM --> Store
  Store --> Engine
  Store --> Repo
  DS --> Repo
  IOSRepo --> Repo

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Data Flow

sequenceDiagram
    participant UI as Compose UI (shared)
    participant Store as CalculatorStore (shared)
    participant Engine as CalculatorEngine (shared)
    participant History as HistoryRepository (platform)

    UI->>Store: onAction(CalculatorAction)
    Store->>Engine: evaluate(...) / toggleLastOperandSign(...)
    Engine-->>Store: EvaluationResult / updated expression
    Store->>History: addHistory(...)
    Store-->>UI: uiState (StateFlow)
    Store-->>UI: invalidExpressionEvents (SharedFlow)

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iOS setup notes

• ./gradlew :shared:podspec :shared:generateDummyFramework
• cd iosApp && pod install
• Open iosApp.xcworkspace
• If Xcode reports a sandbox error for CocoaPods scripts, disable User Script Sandboxing for both iosApp and Pods-iosApp targets.