feat: 完善日报图片与公众号消息展示

修复日报图片读取格式与模型不支持时的友好降级
恢复话题关键词回退，确保词云在缺少顶层关键词时仍可展示
支持公众号多文章消息在聊天、日报、检索和 HTML 导出中完整呈现
迁移账号身份缓存并优化首次连接的账号占位信息
补充图片、词云、账号缓存与多文章消息回归测试

tests/unit/group-report.test.ts

@@ -0,0 +1,46 @@
+import { describe, expect, it } from 'vitest'
+import { parseGroupDailyReport } from '../../src/renderer/src/utils/group-report'
+import type { GroupReportMetadata } from '../../src/shared/group-report'
+
+const metadata: GroupReportMetadata = {
+  groupName: '测试群',
+  reportDate: '2026-08-06',
+  dateRange: '今日',
+  messageCount: 3,
+  activeUsers: 2,
+  timeSpan: '1 h',
+  generatedAt: '2026/8/6 12:00:00',
+  recordNote: 'fixture',
+  footerNote: '',
+  heroParticipants: [],
+  reportMode: 'full'
+}
+
+const media = {
+  gallery: [],
+  voiceHighlights: [],
+  funBadges: []
+}
+
+describe('group report parsing', () => {
+  it('falls back to topic keywords when the model omits top-level keywords', () => {
+    const report = parseGroupDailyReport(
+      JSON.stringify({
+        topics: [
+          {
+            title: '健身安排',
+            summary: '讨论训练时间和肌酸。',
+            keywords: ['肌酸', '训练']
+          }
+        ]
+      }),
+      [],
+      '',
+      [],
+      metadata,
+      media
+    )
+
+    expect(report.keywords).toEqual(['肌酸', '训练', '健身安排'])
+  })
+})