feat(#369): rewrite channels tab with full backend integration (#417)

* feat(#369): rewrite channels tab with full backend integration

- Add state, error, gateway_running, description to model
- Add test endpoint to API service
- Rewrite ViewModel with toggle, restart, test actions
- Rewrite screen with state badges, restart banner, test button
- Fix string resources and E2E test

* fix(#417): add missing import and fix ButtonSize API

- Add MessagingPlatformTestResult import to HermesApiService.kt
- Replace ButtonDefaults.ButtonSize.SMALL with ButtonDefaults.SmallButtonSize (correct M3 API)

* fix(#417): mark platformStateStyle as @Composable, remove Button size param
- @Composable annotation needed for MaterialTheme.colorScheme access
- Button/OutlinedButton size parameter not available in project's M3 version
- ktlint removed unused ButtonDefaults import

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Co-authored-by: M57 <hy4ri@users.noreply.github.com>

app/src/main/java/com/m57/hermescontrol/data/remote/HermesApiService.kt

@@ -17,6 +17,7 @@ import com.m57.hermescontrol.data.model.LogResponse
 import com.m57.hermescontrol.data.model.McpServerToggleRequest
 import com.m57.hermescontrol.data.model.McpServersResponse
 import com.m57.hermescontrol.data.model.MessagingPlatformResponse
+import com.m57.hermescontrol.data.model.MessagingPlatformTestResult
 import com.m57.hermescontrol.data.model.MessagingPlatformUpdate
 import com.m57.hermescontrol.data.model.ModelOptionsResponse
 import com.m57.hermescontrol.data.model.PairingApproveRequest
@@ -260,6 +261,11 @@ interface HermesApiService {
         @Body config: MessagingPlatformUpdate,
     ): Response<Unit>
 
+    @POST("api/messaging/platforms/{platform_id}/test")
+    suspend fun testMessagingPlatform(
+        @Path("platform_id") platformId: String,
+    ): Response<MessagingPlatformTestResult>
+
     @GET("api/env")
     suspend fun getEnvVars(): Response<Map<String, EnvVarConfig>>