feat: 新增群员统计与退群事件，并把本地索引集中到设置页

- 群员统计：档案中按群统计发言排行与未发言成员，可复制纯文本、按平台能力发送
- 退群事件永久保存，并以本地推断条目并入档案消息流
- 设置新增本地索引页，集中管理聊天记录索引与图片文字索引

tests/unit/group-stats-formatter.test.ts

@@ -0,0 +1,172 @@
+import { describe, expect, it } from 'vitest'
+import {
+  formatActiveMemberStats,
+  formatSilentMemberStats,
+  formatStatsDate,
+  formatStatsDateTime,
+  resolveGroupStatsRangeStart,
+  type GroupMemberStatsResult
+} from '../../src/shared/group-stats'
+
+/** 用本地时区构造时间，避免测试受运行机器时区影响。 */
+const at = (year: number, month: number, day: number, hour = 0): number =>
+  new Date(year, month - 1, day, hour).getTime()
+
+const base = (overrides: Partial<GroupMemberStatsResult> = {}): GroupMemberStatsResult => ({
+  conversationId: 'c'.repeat(32),
+  startTime: at(2026, 6, 15),
+  endTime: at(2026, 9, 4),
+  freshness: 'fresh',
+  complete: true,
+  memberCount: 48,
+  activeMemberCount: 45,
+  silentMemberCount: 3,
+  activeMembers: [],
+  silentMembers: [],
+  unattributedMessages: 0,
+  excludedSystemMessages: 0,
+  firstMessageTime: at(2026, 6, 15),
+  limitations: [],
+  ...overrides
+})
+
+describe('GroupStats formatter', () => {
+  it('未发言模板按编号列出，并带区间与人数前缀', () => {
+    const text = formatSilentMemberStats(
+      base({
+        silentMembers: [
+          { senderId: 'wxid_1', displayName: '轩轩', groupNickname: '' },
+          { senderId: 'wxid_2', displayName: '十二', groupNickname: '' },
+          { senderId: 'wxid_3', displayName: '湘江中路', groupNickname: '' }
+        ]
+      })
+    )
+
+    expect(text).toContain('未发言统计')
+    expect(text).toContain('2026-06-15 至 2026-09-04')
+    expect(text).toContain('1. 轩轩')
+    expect(text).toContain('2. 十二')
+    expect(text).toContain('3. 湘江中路')
+    // 纯文本：不能出现 Markdown 标记
+    expect(text).not.toContain('**')
+    expect(text).not.toContain('##')
+  })
+
+  it('未发言模板保留 limitation 文案', () => {
+    const text = formatSilentMemberStats(
+      base({
+        silentMembers: [{ senderId: 'wxid_1', displayName: '轩轩', groupNickname: '' }],
+        limitations: ['统计基于当前群成员名单与本地已归档消息。']
+      })
+    )
+    expect(text).toContain('注：统计基于当前群成员名单与本地已归档消息。')
+  })
+
+  it('未发言为空时给出明确文案而不是空白', () => {
+    const text = formatSilentMemberStats(base())
+    expect(text).toContain('（无）')
+  })
+
+  it('未发言模板支持 limit 并说明省略人数', () => {
+    const silentMembers = Array.from({ length: 5 }, (_, index) => ({
+      senderId: `wxid_${index}`,
+      displayName: `成员${index}`,
+      groupNickname: ''
+    }))
+    const text = formatSilentMemberStats(base({ silentMembers }), { limit: 2 })
+    expect(text).toContain('1. 成员0')
+    expect(text).toContain('2. 成员1')
+    expect(text).not.toContain('3. 成员2')
+    expect(text).toContain('其余 3 人未列出')
+  })
+
+  it('活跃模板带条数', () => {
+    const text = formatActiveMemberStats(
+      base({
+        activeMembers: [
+          {
+            senderId: 'wxid_1',
+            displayName: '张三',
+            groupNickname: '',
+            messageCount: 328,
+            lastMessageTime: at(2026, 9, 20, 12)
+          },
+          {
+            senderId: 'wxid_2',
+            displayName: '李四',
+            groupNickname: '',
+            messageCount: 217,
+            lastMessageTime: at(2026, 9, 19, 12)
+          }
+        ]
+      })
+    )
+
+    expect(text).toContain('群聊活跃统计')
+    expect(text).toContain('统计时间：2026-06-15 至 2026-09-04')
+    expect(text).toContain('1. 张三 328 条')
+    expect(text).toContain('2. 李四 217 条')
+  })
+
+  it('群昵称与主名不同时显示成「微信名（群昵称）」', () => {
+    const text = formatSilentMemberStats(
+      base({
+        silentMembers: [
+          { senderId: 'wxid_1', displayName: '张三', groupNickname: '老张' },
+          // 两者相同时不重复展示，避免噪声
+          { senderId: 'wxid_2', displayName: '李四', groupNickname: '李四' },
+          // 没有群昵称时只显示主名
+          { senderId: 'wxid_3', displayName: '王五', groupNickname: '' }
+        ]
+      })
+    )
+
+    expect(text).toContain('1. 张三（老张）')
+    expect(text).toContain('2. 李四')
+    expect(text).not.toContain('李四（李四）')
+    expect(text).toContain('3. 王五')
+  })
+
+  it('日期格式化使用本地时区且补零', () => {
+    expect(formatStatsDate(at(2026, 1, 5))).toBe('2026-01-05')
+    expect(formatStatsDateTime(at(2026, 1, 5, 9))).toBe('2026-01-05 09:00')
+  })
+
+  it('快捷范围按滑动窗口折算起点', () => {
+    const end = at(2026, 9, 20)
+    expect(resolveGroupStatsRangeStart('7d', end)).toBe(end - 7 * 24 * 60 * 60 * 1000)
+    expect(resolveGroupStatsRangeStart('30d', end)).toBe(end - 30 * 24 * 60 * 60 * 1000)
+    expect(resolveGroupStatsRangeStart('90d', end)).toBe(end - 90 * 24 * 60 * 60 * 1000)
+  })
+
+  it('「全部」不放下界（startTime = 0）', () => {
+    expect(resolveGroupStatsRangeStart('all', at(2026, 9, 20))).toBe(0)
+  })
+
+  it('选「全部」时区间文案用本机第一条消息的真实日期，而不是 1970-01-01', () => {
+    const text = formatSilentMemberStats(
+      base({
+        startTime: 0,
+        firstMessageTime: at(2020, 2, 2),
+        endTime: at(2026, 9, 20),
+        silentMembers: [{ senderId: 'wxid_1', displayName: '轩轩', groupNickname: '' }]
+      })
+    )
+    expect(text).toContain('2020-02-02 至 2026-09-20')
+    expect(text).not.toContain('1970')
+    expect(text).not.toContain('全部历史')
+  })
+
+  it('选「全部」但取不到第一条消息时，退化成「全部历史」且不假装从 1970 开始', () => {
+    const text = formatSilentMemberStats(
+      base({
+        startTime: 0,
+        firstMessageTime: null,
+        endTime: at(2026, 9, 20),
+        silentMembers: [{ senderId: 'wxid_1', displayName: '轩轩', groupNickname: '' }]
+      })
+    )
+    expect(text).toContain('全部历史')
+    expect(text).not.toContain('1970')
+  })
+})