docs: add tests/ folder convention for test output

docs/TESTING-FRAMEWORK.md

@@ -337,6 +337,37 @@ mosis-designer.exe --simulator --test-apps base-apps \
 
 ---
 
+## Test Output Directory
+
+All test files and output should be placed in the `tests/` folder at the project root:
+
+```
+MosisService/
+└── tests/
+    ├── test_navigation.json      # Test action files
+    ├── test_settings.json
+    ├── screenshot_home.png       # Screenshot output
+    ├── screenshot_settings.png
+    ├── hierarchy.json            # Hierarchy dumps
+    └── recorded_actions.json     # Recorded actions
+```
+
+### Usage
+
+```bash
+# Run test with output to tests/ folder
+mosis-designer.exe --simulator --test-apps base-apps \
+    --playback tests/test_navigation.json \
+    --screenshot-after tests/screenshot_result.png \
+    --hierarchy tests/hierarchy.json
+```
+
+This keeps the project root clean and organizes all testing artifacts in one place.
+
+**Note**: The `tests/` folder is gitignored - test outputs are not committed to version control.
+
+---
+
 ## Troubleshooting
 
 ### Tap not registering