refactor: extract stateInUi helper to reduce ViewModel boilerplate

[muraki-sports]

Summary

Introduces a stateInUi() extension function in core:ui to eliminate the repetitive stateIn(scope = viewModelScope, started = SharingStarted.WhileSubscribed(5_000), ...) pattern used across all ViewModels.

Related prior attempt: #454

Changes

New file

• core/ui/FlowExtensions.kt — adds context(viewModel: ViewModel) fun <T> Flow<T>.stateInUi(initialValue: T): StateFlow<T>, a shorthand for the standard UI state flow pattern.

Build

• build-logic/KotlinAndroid.kt — enables the -Xcontext-parameters compiler flag (experimental, Kotlin 2.x) required by the context receiver declaration.
• core/ui/build.gradle.kts — adds androidx.lifecycle.viewModelCompose dependency to resolve viewModelScope inside the extension.

Refactoring

Replaces all stateIn(...) call sites with stateInUi(initialValue = ...) in:

• app — MainActivityViewModel
• feature/bookmarks — BookmarksViewModel
• feature/foryou — ForYouViewModel
• feature/interests — InterestsViewModel
• feature/search — SearchViewModel
• feature/settings — SettingsViewModel
• feature/topic — TopicViewModel

Motivation

Every ViewModel repeated the same three-argument stateIn boilerplate. Extracting it into a named helper:

• removes ~4 lines per call site (net: −75 lines / +71 lines across the codebase)
• makes the intent clearer — stateInUi signals "this is a UI-scoped state flow"
• makes future changes to the sharing strategy (timeout, started policy) a single-line fix

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[gemini-code-assist]

Code Review

This pull request introduces a stateInUi extension function in the core:ui module to standardize the conversion of Flow to StateFlow within ViewModels, leveraging the experimental Kotlin context parameters feature. This utility simplifies code across multiple ViewModels by encapsulating the common WhileSubscribed sharing strategy. Review feedback recommends changing the ViewModel dependency from implementation to api to prevent compilation issues in consumer modules and suggests improving the extension function's flexibility by parameterizing the sharing policy and extracting magic numbers.

[gemini-code-assist]

Since ViewModel is used in the public signature of the stateInUi extension function (as a context parameter), this dependency should be declared as api instead of implementation. This ensures that consumer modules have access to the ViewModel type during compilation when they use this extension.

    api(libs.androidx.lifecycle.viewModelCompose)

[gemini-code-assist]

Consider extracting the 5_000 timeout into a named constant to avoid magic numbers and improve maintainability. Additionally, making the SharingStarted policy an optional parameter provides flexibility for ViewModels that might require a different sharing strategy (e.g., Eagerly or a different timeout) while keeping the common UI pattern concise.

private const val StopTimeoutMillis = 5_000L

context(viewModel: ViewModel)
fun <T> Flow<T>.stateInUi(
    initialValue: T,
    started: SharingStarted = SharingStarted.WhileSubscribed(StopTimeoutMillis),
): StateFlow<T> = stateIn(
    scope = viewModel.viewModelScope,
    started = started,
    initialValue = initialValue,
)