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/data/model/MessagingPlatformResponse.kt

@@ -0,0 +1,7 @@
+package com.m57.hermescontrol.data.model
+
+data class MessagingPlatformResponse(
+    val env_path: String,
+    val gateway_start_command: String,
+    val platforms: List<MessagingPlatform>,
+)