Add WebConfig for static resource handling

Introduced WebConfig to configure resource handling in the backend. This ensures SPA fallback by serving `index.html` for non-existent paths, improving routing for client-side applications.

backend/src/main/java/com/alttd/altitudeweb/config/WebConfig.java

@@ -0,0 +1,33 @@
+package com.alttd.altitudeweb.config;
+
+import org.springframework.context.annotation.Configuration;
+import org.springframework.core.io.ClassPathResource;
+import org.springframework.core.io.Resource;
+import org.springframework.web.servlet.config.annotation.ResourceHandlerRegistry;
+import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;
+import org.springframework.web.servlet.resource.PathResourceResolver;
+
+import java.io.IOException;
+
+@Configuration
+public class WebConfig implements WebMvcConfigurer {
+
+    @Override
+    public void addResourceHandlers(ResourceHandlerRegistry registry) {
+        registry.addResourceHandler("/**")
+                .addResourceLocations("classpath:/static/")
+                .resourceChain(true)
+                .addResolver(new PathResourceResolver() {
+                    @Override
+                    protected Resource getResource(String resourcePath, Resource location) throws IOException {
+                        Resource requestedResource = location.createRelative(resourcePath);
+
+                        if (requestedResource.exists() && requestedResource.isReadable()) {
+                            return requestedResource;
+                        }
+
+                        return new ClassPathResource("/static/index.html");
+                    }
+                });
+    }
+}