feat: add group join approval flow with requireApproval setting

- New join_requests PocketBase collection for pending join applications
- Group requireApproval field (default true) with owner toggle
- JoinGroupDialog: apply when approval required, direct join when not
- JoinRequestCard component for accept/reject in notifications and group panel
- NotificationPanel shows both invitations and join requests
- GroupMembersPanel shows pending requests and approval switch for owners

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/src/api/groups.ts

@@ -1,6 +1,6 @@
 // src/api/groups.ts
 import pb from './pocketbase'
-import type { Group } from '@/types'
+import type { Group, JoinRequest } from '@/types'
 
 // 创建群组
 export async function createGroup(data: {
@@ -14,7 +14,8 @@ export async function createGroup(data: {
   return pb.collection('groups').create({
     ...data,
     owner: user.id,
-    members: [user.id]
+    members: [user.id],
+    requireApproval: true
   })
 }
 
@@ -23,7 +24,6 @@ export async function getUserGroups(): Promise<Group[]> {
   const user = pb.authStore.model
   if (!user) return []
 
-  // 通过 members 字段过滤
   return pb.collection('groups').getList(1, 50, {
     filter: `members ~ "${user.id}"`
   }).then(res => res.items as unknown as Group[])
@@ -36,7 +36,7 @@ export async function getGroup(groupId: string): Promise<Group> {
   }) as unknown as Group
 }
 
-// 加入群组
+// 直接加入群组（无需审核时调用）
 export async function joinGroup(groupId: string) {
   const user = pb.authStore.model
   if (!user) throw new Error('未登录')
@@ -57,6 +57,80 @@ export async function joinGroup(groupId: string) {
   })
 }
 
+// 提交加入申请
+export async function createJoinRequest(groupId: string): Promise<JoinRequest> {
+  const user = pb.authStore.model
+  if (!user) throw new Error('未登录')
+
+  // 检查是否已有待审核的申请
+  const existing = await pb.collection('join_requests').getList(1, 1, {
+    filter: `group="${groupId}" && user="${user.id}" && status="pending"`
+  })
+  if (existing.items.length > 0) {
+    throw new Error('已提交过申请，请等待审核')
+  }
+
+  return pb.collection('join_requests').create({
+    group: groupId,
+    user: user.id,
+    status: 'pending'
+  }) as unknown as JoinRequest
+}
+
+// 获取群组的待审核申请（群主用）
+export async function getGroupJoinRequests(groupId: string): Promise<JoinRequest[]> {
+  const result = await pb.collection('join_requests').getList(1, 50, {
+    filter: `group="${groupId}" && status="pending"`,
+    sort: '-created',
+    expand: 'user'
+  })
+  return result.items as unknown as JoinRequest[]
+}
+
+// 获取我作为群主的所有群组的待审核申请
+export async function getMyGroupsJoinRequests(): Promise<JoinRequest[]> {
+  const user = pb.authStore.model
+  if (!user) return []
+
+  const result = await pb.collection('join_requests').getList(1, 50, {
+    filter: `group.owner="${user.id}" && status="pending"`,
+    sort: '-created',
+    expand: 'user,group'
+  })
+  return result.items as unknown as JoinRequest[]
+}
+
+// 审批加入申请
+export async function respondJoinRequest(
+  requestId: string,
+  status: 'approved' | 'rejected',
+  rejectReason?: string
+) {
+  const updateData: Record<string, unknown> = { status }
+  if (status === 'rejected' && rejectReason) {
+    updateData.rejectReason = rejectReason
+  }
+
+  const request = await pb.collection('join_requests').update(requestId, updateData) as any
+
+  // 如果同意，将用户加入群组
+  if (status === 'approved') {
+    const group = await pb.collection('groups').getOne(request.group) as any
+    const members: string[] = group.members || []
+    if (!members.includes(request.user)) {
+      members.push(request.user)
+      await pb.collection('groups').update(request.group, { members })
+    }
+  }
+
+  return request
+}
+
+// 更新群组审核设置
+export async function updateGroupApproval(groupId: string, requireApproval: boolean) {
+  return pb.collection('groups').update(groupId, { requireApproval })
+}
+
 // 退出群组
 export async function leaveGroup(groupId: string) {
   const user = pb.authStore.model
@@ -97,12 +171,21 @@ export function subscribeGroup(groupId: string, callback: (group: Group) => void
   })
 }
 
+// 订阅加入申请变更
+export function subscribeJoinRequests(groupId: string, callback: (request: JoinRequest) => void) {
+  return pb.collection('join_requests').subscribe('*', (payload) => {
+    const record = payload.record as any
+    if (record.group === groupId) {
+      callback(record as unknown as JoinRequest)
+    }
+  })
+}
+
 // 获取群组成员
 export async function getGroupMembers(groupId: string) {
   const group = await getGroup(groupId)
   const members = group.members as string[]
 
-  // 批量获取用户信息
   const users = await pb.collection('users').getList(1, 50, {
     filter: members.map(id => `id="${id}"`).join(' || ')
   })