feat: Conditionally show 'AI stopped' toast

The 'The AI stopped Screen Operator' toast is now only displayed if:
- 'takeScreenshot()' is not in the AI message (case-insensitive).
- AND the PhotoReasoning screen is not visible.

To check if the app is in the foreground, the ActivityManager is used to analyze running processes. This is a standard Android method to determine the foreground status without requiring additional flags or lifecycle changes in other files.

Fixes unresolved reference to receiverContext.

Author: google-labs-jules[bot]

app/src/main/kotlin/com/google/ai/sample/feature/multimodal/PhotoReasoningViewModel.kt

@@ -134,6 +134,11 @@ class PhotoReasoningViewModel(
                 val errorMessage = intent.getStringExtra(ScreenCaptureService.EXTRA_AI_ERROR_MESSAGE)
 
                 if (responseText != null) {
+                    if (context == null) {
+                        Log.e(TAG, "Context null in receiver, cannot show toast")
+                        return
+                    }
+                    val receiverContext = context
                     Log.d(TAG, "AI Call Success via Broadcast: $responseText")
                     _uiState.value = PhotoReasoningUiState.Success(responseText)
                     updateAiMessage(responseText) // Existing method to update chat history