Feature Request: Add skills for Android architecture best practices

[kevin7254]

Feature Request

Ideally we should have several SKILLS.md for Google recommended Android architecture practices, as mentioned on the page here:
https://developer.android.com/topic/architecture/recommendations

Ideally it should probably be several SKILLS.md separated per layer (One SKILLS.md for UI layer, one for data layer, one for testing and so on..) to not fill the agent with unnecessary context.

Much like it already is on the page above.

[sherviiin]

I've added skills and refs based on existing structure here: b02552f
It follows the same 2 & 3 layer architecture recommended that we know.

4 skills covering Google's recommended Android app architecture, each with a SKILL.md and backing reference docs from developer.android.com:

app-architecture -- Three-layer model, core principles, DI, modularization
data-layer -- Repositories, data sources, SSOT, threading, error handling
domain-layer -- Use cases, when to add them, scoping, lifecycle
ui-layer -- ViewModels, UiState, UDF, events-as-state, state holders, lifecycle

Side note:
I checked NIA to see how compatible that project is and here is the report:
Nia is fully aligned on the core principles of reccomended architecture and orchestration on the following topics:

1. Hilt for dependency injection
2. StateFlow with WhileSubscribed(5_000)
3. One-time events modeled as state (not Channel/SharedFlow)
4. collectAsStateWithLifecycle() everywhere
5. Repository pattern wrapping data sources
6. Use cases with operator fun invoke()
7. Use cases unscoped (no @singleton)
8. VerbNounUseCase naming
9. Navigation 3
10. Fakes over mocks (zero Mockito)
11. No AndroidViewModel
12. Plain state holders (NiaAppState with @stable + remember)
13. Single-activity architecture
14. ViewModel not passed to child composables

It only deviates on the followings:

1. Stream naming: NIA uses observeAll(), observeAllForFollowedTopics() instead of the docs' recommended get{Model}Stream() convention.
2. Multiple StateFlows per ViewModel: ForYouViewModel exposes 4 separate flows (feedState, onboardingUiState, isSyncing, deepLinkedNewsResource) rather than a single bundled UiState. The docs default to single stream but allow multiple for unrelated data.

cc: @JoseAlcerreca / @simona-anomis / @kkuan2011