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/res/values/strings.xml

@@ -375,6 +375,10 @@
     <string name="channels_sec_keys">Configured Keys:</string>
     <string name="channels_status_configured">Configured</string>
     <string name="channels_status_not_set">Not set</string>
+    <string name="channels_action_test">Test</string>
+    <string name="channels_action_restart_now">Restart now</string>
+    <string name="channels_restart_banner">Changes saved. Restart the gateway for them to take effect.</string>
+    <string name="channels_gateway_offline">The gateway is not running. Configure channels here, then restart it.</string>
 
     <!-- Settings -->
     <string name="settings_action_delete_profile">Delete</string>