fix: implement proper executor shutdown for CRITICAL-004

- Add proper ocrExecutor lifecycle management in ScreenCaptureService.onDestroy()
- Use awaitTermination() with 5-second timeout before forcing shutdownNow()
- Handle InterruptedException with proper thread interrupt restoration
- Verified temporary executors in YOLOOnnxDetector already have proper cleanup
- Prevents thread pool resource leaks and ensures clean service shutdown

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

app/src/main/java/com/quillstudios/pokegoalshelper/ScreenCaptureService.kt

@@ -1254,7 +1254,18 @@ class ScreenCaptureService : Service() {
         enhancedFloatingFAB?.hide()
         detectionController.clearUICallbacks()
         yoloDetector?.release()
+        // Proper executor shutdown with timeout
         ocrExecutor.shutdown()
+        try {
+            if (!ocrExecutor.awaitTermination(5, TimeUnit.SECONDS)) {
+                Log.w(TAG, "OCR executor did not terminate gracefully, forcing shutdown")
+                ocrExecutor.shutdownNow()
+            }
+        } catch (e: InterruptedException) {
+            Log.w(TAG, "Interrupted while waiting for OCR executor termination")
+            ocrExecutor.shutdownNow()
+            Thread.currentThread().interrupt()
+        }
         stopScreenCapture()
     }
 }