fix: suppress stack trace on 404 NoResourceFoundException

Add a @RestControllerAdvice that catches NoResourceFoundException and
returns a clean 404 with a single DEBUG log instead of a full stack trace.
Handles browser devtools requests for .js.map files and similar missing
static resources.

src/main/java/dev/kruhlmann/imgfloat/config/GlobalExceptionHandler.java

@@ -0,0 +1,22 @@
+package dev.kruhlmann.imgfloat.config;
+
+import jakarta.servlet.http.HttpServletRequest;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.springframework.http.HttpStatus;
+import org.springframework.http.ResponseEntity;
+import org.springframework.web.bind.annotation.ExceptionHandler;
+import org.springframework.web.bind.annotation.RestControllerAdvice;
+import org.springframework.web.servlet.resource.NoResourceFoundException;
+
+@RestControllerAdvice
+public class GlobalExceptionHandler {
+
+    private static final Logger LOG = LoggerFactory.getLogger(GlobalExceptionHandler.class);
+
+    @ExceptionHandler(NoResourceFoundException.class)
+    public ResponseEntity<Void> handleNoResource(NoResourceFoundException ex, HttpServletRequest request) {
+        LOG.debug("404 Not Found: {}", request.getRequestURI());
+        return ResponseEntity.status(HttpStatus.NOT_FOUND).build();
+    }
+}