chore(idea): mark tests/ as a test source root

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.idea/image-api.iml

@@ -3,6 +3,7 @@
   <component name="NewModuleRootManager">
     <content url="file://$MODULE_DIR$">
       <sourceFolder url="file://$MODULE_DIR$/src" isTestSource="false" />
+      <sourceFolder url="file://$MODULE_DIR$/tests" isTestSource="true" />
       <excludeFolder url="file://$MODULE_DIR$/.idea/dataSources" />
       <excludeFolder url="file://$MODULE_DIR$/target" />
     </content>