Refactor: Extract boilerplate: safeLaunchLoad, clearToast, ToastEffect (CODE-21/22/23) (#312)

- Extracted `safeLaunchLoad` inline extension function to `ViewModelExt.kt` to encapsulate API call success/failure handling logic and replaced usages across 18 viewmodels.
- Extracted `ToastHost` interface to standardize `clearToast()` behavior across all ViewModels displaying toasts.
- Extracted `ToastEffect` composable to `SharedComponents.kt` and applied it to 16 screens, reducing repetitive side effect code blocks.

Fixes #286

app/src/main/java/com/m57/hermescontrol/ui/common/SharedComponents.kt

@@ -343,3 +343,19 @@ fun InfoRow(
         )
     }
 }
+
+// ── ToastEffect — helper for one-shot toast messages ───────────────────
+
+@Composable
+fun ToastEffect(
+    toastMessage: String?,
+    onClearToast: () -> Unit,
+) {
+    val context = androidx.compose.ui.platform.LocalContext.current
+    androidx.compose.runtime.LaunchedEffect(toastMessage) {
+        toastMessage?.let { msg ->
+            android.widget.Toast.makeText(context, msg, android.widget.Toast.LENGTH_SHORT).show()
+            onClearToast()
+        }
+    }
+}

app/src/main/java/com/m57/hermescontrol/ui/common/ViewModelExt.kt

@@ -0,0 +1,28 @@
+package com.m57.hermescontrol.ui.common
+
+import androidx.lifecycle.ViewModel
+import androidx.lifecycle.viewModelScope
+import com.m57.hermescontrol.data.remote.NetworkResult
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.launch
+import kotlinx.coroutines.withContext
+
+interface ToastHost {
+    fun clearToast()
+}
+
+inline fun <T> ViewModel.safeLaunchLoad(
+    crossinline apiCall: suspend () -> NetworkResult<T>,
+    crossinline onStart: () -> Unit,
+    crossinline onSuccess: (T) -> Unit,
+    crossinline onError: (String) -> Unit,
+) {
+    onStart()
+    viewModelScope.launch {
+        val result = withContext(Dispatchers.IO) { apiCall() }
+        when (result) {
+            is NetworkResult.Success -> onSuccess(result.data)
+            is NetworkResult.Failure -> onError(result.error.message ?: "Unknown error")
+        }
+    }
+}