test: add comprehensive test suite for Matches & Ratings API

- Created matches.test.js with 24 tests covering:
  * Match creation and validation
  * Match listing and filtering
  * Match acceptance workflow
  * Match deletion
  * Rating creation and validation
  * User ratings display

- Fixed Jest ES module issues:
  * Added mock for jsdom to bypass parse5 compatibility
  * Added mock for dompurify for test environment
  * Updated package.json with moduleNameMapper

Test results: 19/24 passing (79%)
Remaining: 5 tests need investigation

backend/src/__mocks__/dompurify.js

@@ -0,0 +1,11 @@
+// Mock DOMPurify for Jest tests
+// Returns a sanitize function that just returns the input (for testing)
+
+module.exports = () => ({
+  sanitize: (dirty) => {
+    if (typeof dirty !== 'string') return '';
+    // For tests, just return the string as-is (no actual sanitization)
+    // In real code, this would strip HTML tags
+    return dirty;
+  },
+});

backend/src/__mocks__/jsdom.js

@@ -0,0 +1,50 @@
+// Mock JSDOM for Jest tests
+// This avoids ES module issues with parse5
+
+class MockWindow {
+  constructor() {
+    this.document = {
+      createElement: (tag) => ({
+        setAttribute: () => {},
+        getAttribute: () => null,
+        tagName: tag.toUpperCase(),
+        attributes: {},
+        childNodes: [],
+        appendChild: () => {},
+      }),
+      createTextNode: (text) => ({ textContent: text }),
+      implementation: {
+        createHTMLDocument: () => ({
+          body: {
+            innerHTML: '',
+            appendChild: () => {},
+          },
+        }),
+      },
+    };
+
+    // Add global constructors that DOMPurify needs
+    this.Element = class Element {};
+    this.DocumentFragment = class DocumentFragment {};
+    this.HTMLTemplateElement = class HTMLTemplateElement {};
+    this.Node = class Node {
+      static ELEMENT_NODE = 1;
+      static TEXT_NODE = 3;
+    };
+    this.NodeFilter = {
+      SHOW_ALL: 0xffffffff,
+      SHOW_ELEMENT: 0x1,
+      SHOW_TEXT: 0x4,
+    };
+  }
+}
+
+class MockJSDOM {
+  constructor() {
+    this.window = new MockWindow();
+  }
+}
+
+module.exports = {
+  JSDOM: MockJSDOM,
+};