M2b: Android skeleton, :core:model contract, :domain passing all vectors

Gradle project in android/ with every module of SPEC §6.2 (build-logic convention plugins, version catalog,
architecture check in check), :core:model types and repository interfaces of §14.2.4 and §14.5, :domain
implementing §14.5.2 and §14.5.4 (125 vector cases), scenario-driven fakes with the empty scenario, Room 3
entities and KvittDatabase v1 with exported schema, :app shell with Hilt, en/sv strings with MissingTranslation
as a lint error, Roborazzi goldens of the empty screen in light and dark.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

android/README.md

@@ -0,0 +1,60 @@
+# Kvitt Android project
+
+One Gradle project, modules as in SPEC §6.2 and §14.7. Build only through `tools/gradle-serial.sh` with
+`PATH=/opt/homebrew/opt/openjdk@25/bin:$PATH` (CLAUDE.md › Build and verify). The gate is `tools/gradle-serial.sh check`:
+compile, unit tests (including every vector of `contracts/test-vectors/`), lint (`MissingTranslation` and
+`ExtraTranslation` are errors), the architecture check and the screenshot tests.
+
+## Modules
+
+| Module | Plugin (build-logic) | Notes |
+|---|---|---|
+| `:core:model` | `kvitt.jvm.library` | UI contract (§14.2.4), domain types `model.money` (§14.5.1), analytics types `model.analytics` (§14.5.4) |
+| `:domain` | `kvitt.jvm.library` | §14.5 functions; `VectorTest` runs every vector file, copied by `:domain:copyTestVectors` |
+| `:core:design` | `kvitt.android.library` + `kvitt.android.compose` | `KvittTheme` placeholder; M6 owns the module |
+| `:core:fakes` | `kvitt.android.library` | `FakeRepositories(scenario)`, `FakeScenarios.empty`; scenarios of feature X go in `fakes/<x>/` |
+| `:data` | `kvitt.android.library` + KSP + Room 3 | Room entities and `KvittDatabase` v1, schema in `data/schemas/`; M5 owns the module |
+| `:adapter:fcm` | `kvitt.android.library` | shell; M8 owns it |
+| `:feature:*` | `kvitt.android.feature` | shells with one entry composable; M7a to M7f own them |
+| `:app` | `kvitt.android.application` + compose + hilt + Roborazzi | Application, MainActivity, goldens in `app/src/test/screenshots/` |
+
+## Architecture check
+
+`architectureCheck` runs in every module's `check` (`build-logic/.../ArchitectureRules.kt` holds the rules as data).
+It fails on a project dependency outside the §6.2 table, on `:core:fakes` in any configuration that is not a test or
+debug configuration, and, in `:core:model` and `:domain`, on an Android plugin, on a library outside
+`org.jetbrains.kotlin*`, and on any import or fully qualified reference outside `kotlin.*`, `kotlinx.*` and
+`se.hagstedt.kvitt.*` in `src/main`. A new module must be added to `ArchitectureRules.allowed`.
+
+## Feature convention
+
+* Each feature module exposes **one composable entry point per screen**. By default it obtains its ViewModel with
+  `hiltViewModel()` (from `androidx.hilt:hilt-lifecycle-viewmodel-compose`) and takes navigation as plain lambdas,
+  for example:
+
+  ```kotlin
+  @Composable
+  fun AccountDetailScreen(
+      onOpenExpense: (ExpenseId) -> Unit,
+      onAddExpense: (AccountId) -> Unit,
+      onBack: () -> Unit,
+      modifier: Modifier = Modifier,
+      viewModel: AccountDetailViewModel = hiltViewModel(),
+  )
+  ```
+
+  A stateless overload that takes the `*State` and event lambdas is what previews and screenshot tests render.
+* ViewModels are `@HiltViewModel` classes that receive repositories **through the interfaces of `:core:model`** only.
+  `:app` binds those interfaces to `:data` (release) or `:core:fakes` (debug and tests) with Hilt (M8).
+* Features never reference another feature, the `NavHost` or `:data`/`:domain`. `:app` owns the `NavHost` and wires
+  the lambdas.
+* Strings live in the feature's own `src/main/res/values/strings.xml` and `values-sv/strings.xml`, keys prefixed with
+  the feature name; shared strings in `:core:design`; `:app` holds only the app name.
+* Previews and screenshot tests use `FakeRepositories(scenario)` from `:core:fakes` (`debugImplementation` and
+  `testImplementation`, added by the feature plugin). Fakes never reach a release build.
+
+## Screenshot tests
+
+Roborazzi on Robolectric. `roborazzi.test.verify=true` in `gradle.properties` makes every unit-test run compare with the
+committed goldens. Re-record an intended change with `tools/gradle-serial.sh recordRoborazziDebug` and open every
+changed PNG before committing.