feat(characters:domain): models + CharacterRepository interface (REDI-85)

- Character, CharacterStatus, CharactersPage(characters, nextPage), CharacterDetails.
- CharacterRepository interface returning Result<CharactersPage, DataError> and
  Result<CharacterDetails, DataError>. Pure Kotlin, no serialization annotations, no Android.

feature/characters/domain/src/main/kotlin/com/example/architecture/feature/characters/domain/CharacterRepository.kt

@@ -0,0 +1,17 @@
+package com.example.architecture.feature.characters.domain
+
+import com.example.architecture.core.domain.DataError
+import com.example.architecture.core.domain.Result
+import com.example.architecture.feature.characters.domain.model.CharacterDetails
+import com.example.architecture.feature.characters.domain.model.CharactersPage
+
+/**
+ * Contract for the characters data layer. Lives in domain so presentation never depends on data.
+ * Returns the [DataError] supertype because an implementation may merge sources (e.g. an
+ * offline-first repository combining network + local).
+ */
+interface CharacterRepository {
+    suspend fun getCharacters(page: Int): Result<CharactersPage, DataError>
+
+    suspend fun getCharacterDetails(id: Int): Result<CharacterDetails, DataError>
+}

feature/characters/domain/src/main/kotlin/com/example/architecture/feature/characters/domain/model/Character.kt

@@ -0,0 +1,10 @@
+package com.example.architecture.feature.characters.domain.model
+
+/** A character as shown in the list. */
+data class Character(
+    val id: Int,
+    val name: String,
+    val status: CharacterStatus,
+    val species: String,
+    val imageUrl: String,
+)

feature/characters/domain/src/main/kotlin/com/example/architecture/feature/characters/domain/model/CharacterDetails.kt

@@ -0,0 +1,15 @@
+package com.example.architecture.feature.characters.domain.model
+
+/** Full character profile shown on the detail screen. */
+data class CharacterDetails(
+    val id: Int,
+    val name: String,
+    val status: CharacterStatus,
+    val species: String,
+    val type: String,
+    val gender: String,
+    val origin: String,
+    val location: String,
+    val imageUrl: String,
+    val episodeCount: Int,
+)

feature/characters/domain/src/main/kotlin/com/example/architecture/feature/characters/domain/model/CharacterStatus.kt

@@ -0,0 +1,8 @@
+package com.example.architecture.feature.characters.domain.model
+
+/** Life status of a character. Mapped from the API's string in the data layer. */
+enum class CharacterStatus {
+    ALIVE,
+    DEAD,
+    UNKNOWN,
+}

feature/characters/domain/src/main/kotlin/com/example/architecture/feature/characters/domain/model/CharactersPage.kt

@@ -0,0 +1,7 @@
+package com.example.architecture.feature.characters.domain.model
+
+/** One page of characters plus the next page index ([nextPage] is null when there are no more). */
+data class CharactersPage(
+    val characters: List<Character>,
+    val nextPage: Int?,
+)