feat: add premium plugin support, custom plugin builder, and comprehensive code improvements

- Add VaadinCKEditorPremium class with @NpmPackage for ckeditor5-premium-features
- Add CustomPlugin.fromPremium() factory and import path validation (SSRF protection)
- Add premium plugin dependency resolution in CKEditorPluginDependencies
- Add document-editor.css for decoupled editor layout
- Enhance vaadin-ckeditor.ts with minimap, document outline, sticky toolbar improvements
- Enhance upload-adapter.ts with timeout, retry, and cleanup on disconnect
- Translate all Chinese comments to English across Java, TypeScript, and CSS files
- Add comprehensive tests for premium features, custom plugins, and upload manager
- Update README and PREMIUM_INTEGRATION docs

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: jet-pang

README.md

@@ -155,7 +155,25 @@ editor.setReadOnly(false);
 
 Premium features require a CKEditor license. Get yours at [ckeditor.com/pricing](https://ckeditor.com/pricing).
 
-### Step 1: Install Premium Package
+### Step 1: Enable Premium Package
+
+**Option A: Use `VaadinCKEditorPremium` class (Recommended)**
+
+Simply call `VaadinCKEditorPremium.enable()` once at application startup to automatically install the premium npm package:
+
+```java
+import com.wontlost.ckeditor.VaadinCKEditorPremium;
+
+@SpringBootApplication
+public class Application implements AppShellConfigurator {
+    public static void main(String[] args) {
+        VaadinCKEditorPremium.enable();  // Enable premium features
+        SpringApplication.run(Application.class, args);
+    }
+}
+```
+
+**Option B: Manual npm installation**
 
 In your Vaadin project's frontend directory:
 

docs/PREMIUM_INTEGRATION.md

@@ -28,9 +28,28 @@ All plans include a **14-day free trial** with full access.
 2. Start a free trial or purchase a plan
 3. Copy your license key from the dashboard
 
-### 2. Install Premium Package
+### 2. Enable Premium Features (Recommended)
 
-In your Vaadin project's `frontend/` directory:
+**Option A: Use `VaadinCKEditorPremium` class (Recommended)**
+
+The simplest way to enable premium features is to call `VaadinCKEditorPremium.enable()` once at application startup. This automatically installs the `ckeditor5-premium-features` npm package:
+
+```java
+import com.wontlost.ckeditor.VaadinCKEditorPremium;
+
+@SpringBootApplication
+public class Application implements AppShellConfigurator {
+    public static void main(String[] args) {
+        // Enable premium features - call once at startup
+        VaadinCKEditorPremium.enable();
+        SpringApplication.run(Application.class, args);
+    }
+}
+```
+
+**Option B: Manual npm installation**
+
+Alternatively, install the package manually in your Vaadin project's `frontend/` directory:
 
 ```bash
 cd frontend
@@ -65,6 +84,23 @@ VaadinCKEditor editor = VaadinCKEditor.create()
     .build();
 ```
 
+### 4. Using PremiumPlugin Enum (Type-Safe)
+
+For type-safe premium plugin configuration, use the `PremiumPlugin` enum:
+
+```java
+import com.wontlost.ckeditor.*;
+import com.wontlost.ckeditor.VaadinCKEditorPremium.PremiumPlugin;
+
+VaadinCKEditor editor = VaadinCKEditor.create()
+    .withPreset(CKEditorPreset.FULL)
+    .withLicenseKey(System.getenv("CKEDITOR_LICENSE_KEY"))
+    .addCustomPlugin(PremiumPlugin.EXPORT_PDF.toCustomPlugin())
+    .addCustomPlugin(PremiumPlugin.EXPORT_WORD.toCustomPlugin())
+    .addCustomPlugin(PremiumPlugin.FORMAT_PAINTER.toCustomPlugin())
+    .build();
+```
+
 ## Premium Plugins Reference
 
 ### Document Conversion

pom.xml

@@ -5,7 +5,7 @@
     <groupId>com.wontlost</groupId>
     <artifactId>ckeditor-vaadin</artifactId>
     <packaging>jar</packaging>
-    <version>5.0.3</version>
+    <version>5.0.4</version>
     <name>CKEditorVaadin</name>
     <description>Integration of CKEditor 5 for Vaadin</description>
     <url>https://github.com/wontlost-ltd/vaadin-ckeditor</url>