Bug/v2/improved cache busting (#5107)

# Description of Changes

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Please provide a summary of the changes, including:

- What was changed
- Why the change was made
- Any challenges encountered

Closes #(issue_number)
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---

## Checklist

### General

- [ ] I have read the [Contribution
Guidelines](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/CONTRIBUTING.md)
- [ ] I have read the [Stirling-PDF Developer
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/DeveloperGuide.md)
(if applicable)
- [ ] I have read the [How to add new languages to
Stirling-PDF](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/HowToAddNewLanguage.md)
(if applicable)
- [ ] I have performed a self-review of my own code
- [ ] My changes generate no new warnings

### Documentation

- [ ] I have updated relevant docs on [Stirling-PDF's doc
repo](https://github.com/Stirling-Tools/Stirling-Tools.github.io/blob/main/docs/)
(if functionality has heavily changed)
- [ ] I have read the section [Add New Translation
Tags](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/HowToAddNewLanguage.md#add-new-translation-tags)
(for new translation tags only)

### Translations (if applicable)

- [ ] I ran
[`scripts/counter_translation.py`](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/docs/counter_translation.md)

### UI Changes (if applicable)

- [ ] Screenshots or videos demonstrating the UI changes are attached
(e.g., as comments or direct attachments in the PR)

### Testing (if applicable)

- [ ] I have tested my changes locally. Refer to the [Testing
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/DeveloperGuide.md#6-testing)
for more details.

app/core/src/main/java/stirling/software/SPDF/config/WebMvcConfig.java

@@ -1,10 +1,14 @@
 package stirling.software.SPDF.config;
 
+import java.util.concurrent.TimeUnit;
+
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 import org.springframework.context.annotation.Configuration;
+import org.springframework.http.CacheControl;
 import org.springframework.web.servlet.config.annotation.CorsRegistry;
 import org.springframework.web.servlet.config.annotation.InterceptorRegistry;
+import org.springframework.web.servlet.config.annotation.ResourceHandlerRegistry;
 import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;
 
 import lombok.RequiredArgsConstructor;
@@ -25,6 +29,20 @@ public class WebMvcConfig implements WebMvcConfigurer {
         registry.addInterceptor(endpointInterceptor);
     }
 
+    @Override
+    public void addResourceHandlers(ResourceHandlerRegistry registry) {
+        // Cache hashed assets (JS/CSS with content hashes) for 1 year
+        // These files have names like index-ChAS4tCC.js that change when content changes
+        registry.addResourceHandler("/assets/**")
+                .addResourceLocations("classpath:/static/assets/")
+                .setCacheControl(CacheControl.maxAge(365, TimeUnit.DAYS).cachePublic());
+
+        // Don't cache index.html - it needs to be fresh to reference latest hashed assets
+        registry.addResourceHandler("/index.html")
+                .addResourceLocations("classpath:/static/")
+                .setCacheControl(CacheControl.noCache().mustRevalidate());
+    }
+
     @Override
     public void addCorsMappings(CorsRegistry registry) {
         // Check if running in Tauri mode