feat: register Slint file type in plugin.xml

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

src/main/resources/META-INF/plugin.xml

@@ -14,6 +14,12 @@
     <!-- Extensions defined by the plugin.
          Read more: https://plugins.jetbrains.com/docs/intellij/plugin-extension-points.html -->
     <extensions defaultExtensionNs="com.intellij">
+        <fileType
+            name="Slint"
+            implementationClass="me.zhouxi.slint.lang.SlintFileType"
+            fieldName="INSTANCE"
+            language="Slint"
+            extensions="slint"/>
         <platform.lsp.serverSupportProvider implementation="me.zhouxi.slint.lsp.SlintLspServerSupportProvider"/>
     </extensions>
 </idea-plugin>