test(08-02): add failing test for formatTimestamp utility

RED phase: Create test file with 6 test cases for timestamp formatting:
- "Just now" for messages within last minute
- "X minutes ago" for messages within last hour
- "X hours ago" for messages within last day
- "Yesterday" for previous day messages
- Date format (MM/DD/YYYY) for older messages
- Graceful handling of invalid dates

Install dayjs for timestamp formatting utility.

Tests fail as expected (utility not implemented yet).

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

jam-ui/package-lock.json

@@ -32,6 +32,7 @@
         "classnames": "^2.2.6",
         "creditcard.js": "^3.0.33",
         "custom-protocol-check": "^1.4.0",
+        "dayjs": "^1.11.19",
         "echarts": "^4.9.0",
         "echarts-for-react": "^2.0.16",
         "element-resize-event": "^3.0.3",
@@ -9496,6 +9497,12 @@
         "webidl-conversions": "^4.0.2"
       }
     },
+    "node_modules/dayjs": {
+      "version": "1.11.19",
+      "resolved": "https://registry.npmjs.org/dayjs/-/dayjs-1.11.19.tgz",
+      "integrity": "sha512-t5EcLVS6QPBNqM2z8fakk/NKel+Xzshgt8FFKAn+qwlD1pzZWxh0nVCrvFK7ZDb6XucZeF9z8C7CBWTRIVApAw==",
+      "license": "MIT"
+    },
     "node_modules/debounce": {
       "version": "1.2.1",
       "resolved": "https://registry.npmjs.org/debounce/-/debounce-1.2.1.tgz",

jam-ui/package.json

@@ -27,6 +27,7 @@
     "classnames": "^2.2.6",
     "creditcard.js": "^3.0.33",
     "custom-protocol-check": "^1.4.0",
+    "dayjs": "^1.11.19",
     "echarts": "^4.9.0",
     "echarts-for-react": "^2.0.16",
     "element-resize-event": "^3.0.3",

jam-ui/src/utils/__tests__/formatTimestamp.test.js

@@ -0,0 +1,35 @@
+import { formatTimestamp } from '../formatTimestamp';
+
+describe('formatTimestamp', () => {
+  test('returns "Just now" for messages within last minute', () => {
+    const now = new Date();
+    expect(formatTimestamp(now.toISOString())).toBe('Just now');
+  });
+
+  test('returns "X minutes ago" for messages within last hour', () => {
+    const fiveMinutesAgo = new Date(Date.now() - 5 * 60 * 1000);
+    expect(formatTimestamp(fiveMinutesAgo.toISOString())).toBe('5 minutes ago');
+  });
+
+  test('returns "X hours ago" for messages within last day', () => {
+    const twoHoursAgo = new Date(Date.now() - 2 * 60 * 60 * 1000);
+    expect(formatTimestamp(twoHoursAgo.toISOString())).toBe('2 hours ago');
+  });
+
+  test('returns "Yesterday" for messages from previous day', () => {
+    const yesterday = new Date(Date.now() - 24 * 60 * 60 * 1000);
+    expect(formatTimestamp(yesterday.toISOString())).toMatch(/Yesterday/);
+  });
+
+  test('returns date for older messages', () => {
+    const lastWeek = new Date(Date.now() - 7 * 24 * 60 * 60 * 1000);
+    const result = formatTimestamp(lastWeek.toISOString());
+    expect(result).toMatch(/\d{1,2}\/\d{1,2}\/\d{4}/); // MM/DD/YYYY format
+  });
+
+  test('handles invalid dates gracefully', () => {
+    expect(formatTimestamp(null)).toBe('');
+    expect(formatTimestamp(undefined)).toBe('');
+    expect(formatTimestamp('invalid')).toBe('');
+  });
+});