add MVI screen pattern skill and ObserverAsEvent helper

[joelkanyi]

Establishes the screen architecture we follow going forward, and ships the small helper the pattern depends on.

What's in

ObserverAsEvent in uicomponent/src/main/java/com/android/swingmusic/uicomponent/presentation/util/. Lifecycle-aware effect collector. Ties collection to the STARTED state and uses Dispatchers.Main.immediate so navigation feels synchronous and effects don't fire while the screen is hidden.

ObserverAsEvent(viewModel.uiEffect) { effect ->
    when (effect) { ... }
}

Added lifecycle-runtime-compose to the version catalog and to uicomponent's deps so we can use androidx.lifecycle.compose.LocalLifecycleOwner and repeatOnLifecycle. Existing lifecycle version (2.8.7) already supports it, no version bump.

.claude/skills/mvi-screen.md — the full pattern with templates for each of the five files (Screen + ScreenContent, ViewModel, UiState, UiEvent, UiEffect). Invoke as /mvi-screen for the templates. Key conventions baked in:

• Initial data fetches go in the VM init { } block. No LaunchedEffect for fetches in the Screen.
• One-shot effects flow through a Channel<UiEffect> and are always collected with ObserverAsEvent. Never raw LaunchedEffect { effects.collect { } }.
• No loadedInitialData flag, the VM lifecycle handles it.
• ScreenContent is stateless so it can be @Previewd. The outer Screen binds the VM and effects.

CLAUDE.md — added a short pointer in the Architecture section so the pattern gets applied on every screen task without needing the skill to be explicitly invoked.

.gitignore — excludes .claude/settings.local.json (local user settings) while keeping the skills folder tracked.

Why now

While working on #104 we noticed the folder screen refetches on every back-nav. Joel asked why, and the answer surfaced that we don't have a standard pattern for "data lives in the VM, screen just reads from it." This PR sets the baseline. Future screen work follows it; existing screens can be migrated incrementally when we touch them.

Not in scope

No existing screens are migrated in this PR. That can happen one screen at a time as we work on each feature.