chore: mock fetch and eventsource in tests

test/setupTests.ts

@@ -1,2 +1,46 @@
 // Adds jest-dom matchers for React testing library
-import '@testing-library/jest-dom';
+import '@testing-library/jest-dom';
+
+// Minimal browser API mocks for the test environment.
+// Fetch
+if (!globalThis.fetch) {
+  globalThis.fetch = jest.fn(async () => ({
+    ok: true,
+    status: 200,
+    json: async () => [],
+    text: async () => '',
+  })) as unknown as typeof fetch;
+}
+
+// EventSource
+if (!globalThis.EventSource) {
+  class MockEventSource {
+    url: string;
+    readyState = 1;
+    onmessage: ((event: MessageEvent) => void) | null = null;
+    onerror: ((event: Event) => void) | null = null;
+    onopen: ((event: Event) => void) | null = null;
+
+    constructor(url: string) {
+      this.url = url;
+    }
+
+    close() {
+      this.readyState = 2;
+    }
+
+    addEventListener(type: string, listener: (event: MessageEvent) => void) {
+      if (type === 'message') {
+        this.onmessage = listener;
+      }
+    }
+
+    removeEventListener(type: string, listener: (event: MessageEvent) => void) {
+      if (type === 'message' && this.onmessage === listener) {
+        this.onmessage = null;
+      }
+    }
+  }
+
+  globalThis.EventSource = MockEventSource as unknown as typeof EventSource;
+}