fix(#201): fix platforms endpoint response shape mismatch

GET /api/messaging/platforms returns a JSON object with a platforms
array inside, but the app expected a bare array. Wraps the response
in a new MessagingPlatformResponse model.

- Adds MessagingPlatformResponse.kt wrapper model
- Updates HermesApiService.kt return type + adds profile query param
- Updates ChannelsViewModel.kt to unwrap .platforms
- Updates E2eIntegrationTest.kt mock to match new response shape

app/src/main/java/com/m57/hermescontrol/ui/channels/ChannelsViewModel.kt

@@ -35,7 +35,7 @@ class ChannelsViewModel : ViewModel() {
                 }
             when (result) {
                 is NetworkResult.Success -> {
-                    _uiState.update { it.copy(isLoading = false, platforms = result.data.orEmpty()) }
+                    _uiState.update { it.copy(isLoading = false, platforms = result.data?.platforms.orEmpty()) }
                 }
 
                 is NetworkResult.Failure -> {