REDI-96: repository MockEngine test + Compose robot UI test + serialization fix

NetworkCharacterRepositoryTest swaps a Ktor MockEngine into HttpClientFactory and
covers success mapping (incl. request URL/page-param construction), 404 ->
NOT_FOUND, 500 -> SERVER_ERROR, and malformed body -> SERIALIZATION. That last
case exposed a real bug: Ktor wraps the kotlinx SerializationException in its own
ContentConvertException, so safeCall mapped it to UNKNOWN; safeCall now scans the
cause chain and maps it to SERIALIZATION. Adds an instrumented Compose UI test
(CharacterListScreen) using the chaining CharacterListRobot: rendered items,
empty/error states, and tap -> Action.

core/data/src/main/kotlin/com/example/architecture/core/data/network/HttpClientExt.kt

@@ -75,8 +75,16 @@ suspend inline fun <reified T> safeCall(
         Result.Error(DataError.Network.SERIALIZATION)
     } catch (e: Exception) {
         if (e is CancellationException) throw e
-        logNetworkError(e, "Unknown network failure")
-        Result.Error(DataError.Network.UNKNOWN)
+        // Ktor's ContentNegotiation wraps a kotlinx SerializationException (malformed/garbage body)
+        // in its own ContentConvertException, so the catch above misses it. Scan the cause chain so a
+        // bad payload still maps to SERIALIZATION instead of the generic UNKNOWN.
+        if (generateSequence(e as Throwable) { it.cause }.any { it is SerializationException }) {
+            logNetworkError(e, "Serialization failure (wrapped)")
+            Result.Error(DataError.Network.SERIALIZATION)
+        } else {
+            logNetworkError(e, "Unknown network failure")
+            Result.Error(DataError.Network.UNKNOWN)
+        }
     }
 }