feat: 멤버 관리 연동 + 사용자 검색 API (3단계)

- 멤버 목록/초대/역할변경/제거 프론트 연동(RepoMembersPage), 초대 자동완성
- GET /users 사용자 검색 API + UserController
- RepoMembersPage 역할 변경 드롭다운 잘림(overflow) 수정
- InviteMember/UpdateMember DTO, RepoMember 엔티티 정비

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/src/composables/useMember.ts

@@ -0,0 +1,47 @@
+import { useApi } from './useApi'
+import type {
+  ApiRepoMember,
+  InviteMemberPayload,
+  UpdateMemberPayload,
+} from '@/types/member'
+
+// 저장소 멤버 도메인 API Composable — 인터셉터가 success/data 를 언래핑
+// 경로는 모두 repoId(slugName) 하위: /repos/:repoId/members
+export function useMember() {
+  const api = useApi()
+
+  // 멤버 목록 (멤버 또는 공개 저장소)
+  async function list(repoId: string): Promise<ApiRepoMember[]> {
+    return (await api.get(`/repos/${repoId}/members`)) as unknown as ApiRepoMember[]
+  }
+
+  // 멤버 초대 (admin) — 가입된 사용자만 이메일로 초대
+  async function invite(
+    repoId: string,
+    payload: InviteMemberPayload,
+  ): Promise<ApiRepoMember> {
+    return (await api.post(
+      `/repos/${repoId}/members`,
+      payload,
+    )) as unknown as ApiRepoMember
+  }
+
+  // 멤버 역할/직무 변경 (admin, owner 제외)
+  async function update(
+    repoId: string,
+    userId: string,
+    payload: UpdateMemberPayload,
+  ): Promise<ApiRepoMember> {
+    return (await api.patch(
+      `/repos/${repoId}/members/${userId}`,
+      payload,
+    )) as unknown as ApiRepoMember
+  }
+
+  // 멤버 제거 (admin, owner 제외)
+  async function remove(repoId: string, userId: string): Promise<void> {
+    await api.delete(`/repos/${repoId}/members/${userId}`)
+  }
+
+  return { list, invite, update, remove }
+}

frontend/src/composables/useUser.ts

@@ -0,0 +1,16 @@
+import { useApi } from './useApi'
+import type { ApiMember } from '@/types/repo'
+
+// 사용자 도메인 API Composable — 멤버 초대 자동완성용 검색/목록
+// 응답은 PublicUser(= ApiMember: { id, email, name, role }) 배열
+export function useUser() {
+  const api = useApi()
+
+  // 사용자 검색 — q 가 있으면 이메일/이름 부분일치, 없으면 전체 목록
+  async function search(q?: string): Promise<ApiMember[]> {
+    const params = q && q.trim() ? { q: q.trim() } : {}
+    return (await api.get('/users', { params })) as unknown as ApiMember[]
+  }
+
+  return { search }
+}