add base-apps with manifests, layout system, and testing documentation

- Rename test-apps to base-apps with proper manifest.json for each app
- Add is_system_app flag to app discovery and Lua API
- Fix icon path resolution for /system/icons/ paths
- Add layout.lua and layout.rcss for reusable UI components
- Update home screen to dynamically load all apps from manifests
- Update all app RML files to use layout components
- Comprehensive testing framework documentation with JSON action format
- Add tests/ directory structure for automated UI testing

designer/main.cpp

@@ -1097,7 +1097,7 @@ bool InitializeRmlUi(const std::string& assets_path, int fb_width, int fb_height
                 lua_pushstring(L, app.GetIconPath().c_str());
                 lua_setfield(L, -2, "icon");
 
-                lua_pushboolean(L, false);  // Not a system app
+                lua_pushboolean(L, app.is_system_app);
                 lua_setfield(L, -2, "is_system_app");
 
                 lua_pushstring(L, app.app_path.c_str());