fix(#372): plugin install/uninstall 400 — enable instead of install for on-disk plugins, gate uninstall behind canRemove, parse FastAPI error bodies (#416)

- Replace installPlugin(name) with activatePlugin(plugin) that calls enable endpoint
  instead of the install endpoint for plugins already on disk (bundled/inactive).
- Gate Uninstall button behind plugin.canRemove — bundled plugins don't show it.
- Update PluginsScreen to call activatePlugin(plugin) instead of installPlugin(name).
- Parse FastAPI 'detail' field from 400 response bodies in mapHttpError/safeApiCall
  so users see the actual error message instead of a generic placeholder.
- Import ButtonDefaults to fix max-line-length lint warning.

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

app/src/main/java/com/m57/hermescontrol/ui/plugins/PluginsScreen.kt

@@ -13,6 +13,7 @@ import androidx.compose.foundation.layout.width
 import androidx.compose.foundation.lazy.LazyColumn
 import androidx.compose.foundation.lazy.items
 import androidx.compose.material3.Button
+import androidx.compose.material3.ButtonDefaults
 import androidx.compose.material3.Card
 import androidx.compose.material3.CircularProgressIndicator
 import androidx.compose.material3.ExperimentalMaterial3Api
@@ -159,18 +160,20 @@ fun PluginsScreen(
                                                 OutlinedButton(onClick = { viewModel.updatePlugin(plugin.name) }) {
                                                     Text(stringResource(R.string.plugins_action_update))
                                                 }
-                                                Spacer(modifier = Modifier.width(8.dp))
-                                                OutlinedButton(
-                                                    onClick = { viewModel.uninstallPlugin(plugin.name) },
-                                                    colors =
-                                                        androidx.compose.material3.ButtonDefaults.outlinedButtonColors(
-                                                            contentColor = MaterialTheme.colorScheme.error,
-                                                        ),
-                                                ) {
-                                                    Text(stringResource(R.string.plugins_action_uninstall))
+                                                if (plugin.canRemove) {
+                                                    Spacer(modifier = Modifier.width(8.dp))
+                                                    OutlinedButton(
+                                                        onClick = { viewModel.uninstallPlugin(plugin.name) },
+                                                        colors =
+                                                            ButtonDefaults.outlinedButtonColors(
+                                                                contentColor = MaterialTheme.colorScheme.error,
+                                                            ),
+                                                    ) {
+                                                        Text(stringResource(R.string.plugins_action_uninstall))
+                                                    }
                                                 }
                                             } else {
-                                                Button(onClick = { viewModel.installPlugin(plugin.name) }) {
+                                                Button(onClick = { viewModel.activatePlugin(plugin) }) {
                                                     Text(stringResource(R.string.plugins_action_install))
                                                 }
                                             }

app/src/main/java/com/m57/hermescontrol/ui/plugins/PluginsViewModel.kt

@@ -79,25 +79,20 @@ class PluginsViewModel : ViewModel(), ToastHost {
         }
     }
 
-    fun installPlugin(name: String) {
+    fun activatePlugin(plugin: PluginInfo) {
         viewModelScope.launch {
             val result =
                 withContext(Dispatchers.IO) {
-                    safeApiCall {
-                        ApiClient.hermesApi.installPlugin(
-                            com.m57.hermescontrol.data.model
-                                .AgentPluginInstallBody(name),
-                        )
-                    }
+                    safeApiCall { ApiClient.hermesApi.enablePlugin(plugin.name) }
                 }
             when (result) {
                 is NetworkResult.Success -> {
-                    _uiState.update { it.copy(toastMessage = "Plugin installed successfully") }
+                    _uiState.update { it.copy(toastMessage = "Plugin enabled successfully") }
                     loadPlugins()
                 }
 
                 is NetworkResult.Failure -> {
-                    _uiState.update { it.copy(toastMessage = "Failed to install plugin: ${result.error.message}") }
+                    _uiState.update { it.copy(toastMessage = "Failed to enable plugin: ${result.error.message}") }
                 }
             }
         }