feat(cfc-backend): add /api/family/member/editable endpoint

New POST endpoint to check if a family member's info is editable (only non-login members with source=family_member).

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

cfc-backend/src/main/java/com/etotem/cfc/controller/family/FamilyMembersController.java

@@ -139,4 +139,20 @@ public class FamilyMembersController {
         List<RelationshipType> types = familyMemberService.getRelationshipTypes();
         return Result.success(types);
     }
+
+    @Operation(summary = "检查成员是否可编辑")
+    @PostMapping("/editable")
+    public Result<Boolean> checkEditable(HttpServletRequest request,
+                                          @RequestBody Map<String, Long> body) {
+        Long userId = getUserId(request);
+        if (userId == null) {
+            return Result.error("请先登录");
+        }
+        Long memberId = body.get("memberId");
+        if (memberId == null) {
+            return Result.error("缺少成员ID");
+        }
+        boolean editable = familyMemberService.isEditable(memberId);
+        return Result.success(editable);
+    }
 }