feat(im-service): 添加群组 HTTP API (GroupController)

- POST /api/im/groups：创建群组（含成员列表）
- GET  /api/im/groups：按 appId 列出群组
- POST /api/im/groups/{groupId}/members：添加成员
- DELETE /api/im/groups/{groupId}/members/{targetUserId}：移除成员
ImGroupService 已有实现，仅补充 controller 层

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

im-service/src/main/java/com/xuqm/im/controller/GroupController.java

@@ -0,0 +1,55 @@
+package com.xuqm.im.controller;
+
+import com.xuqm.common.model.ApiResponse;
+import com.xuqm.im.entity.ImGroupEntity;
+import com.xuqm.im.service.ImGroupService;
+import org.springframework.http.ResponseEntity;
+import org.springframework.security.core.annotation.AuthenticationPrincipal;
+import org.springframework.web.bind.annotation.*;
+
+import java.util.List;
+
+@RestController
+@RequestMapping("/api/im/groups")
+public class GroupController {
+
+    private final ImGroupService groupService;
+
+    public GroupController(ImGroupService groupService) {
+        this.groupService = groupService;
+    }
+
+    @PostMapping
+    public ResponseEntity<ApiResponse<ImGroupEntity>> create(
+            @RequestBody CreateGroupRequest req,
+            @AuthenticationPrincipal String userId,
+            @RequestParam String appId) {
+        return ResponseEntity.ok(ApiResponse.success(
+                groupService.create(appId, req.name(), userId, req.memberIds())));
+    }
+
+    @GetMapping
+    public ResponseEntity<ApiResponse<List<ImGroupEntity>>> list(
+            @RequestParam String appId) {
+        return ResponseEntity.ok(ApiResponse.success(groupService.listByApp(appId)));
+    }
+
+    @PostMapping("/{groupId}/members")
+    public ResponseEntity<ApiResponse<ImGroupEntity>> addMember(
+            @PathVariable String groupId,
+            @RequestBody MemberRequest req,
+            @AuthenticationPrincipal String userId) {
+        return ResponseEntity.ok(ApiResponse.success(groupService.addMember(groupId, req.userId())));
+    }
+
+    @DeleteMapping("/{groupId}/members/{targetUserId}")
+    public ResponseEntity<ApiResponse<ImGroupEntity>> removeMember(
+            @PathVariable String groupId,
+            @PathVariable String targetUserId,
+            @AuthenticationPrincipal String userId) {
+        return ResponseEntity.ok(ApiResponse.success(groupService.removeMember(groupId, targetUserId, userId)));
+    }
+
+    public record CreateGroupRequest(String name, List<String> memberIds) {}
+    public record MemberRequest(String userId) {}
+}