Step UX-1：通用选择器

frontend/src/components/IssueForm.vue

@@ -4,6 +4,9 @@
       <el-form-item label="标题" prop="title">
         <el-input v-model="form.title" />
       </el-form-item>
+      <el-form-item label="受试者">
+        <SubjectSelect v-model="form.subject_id" :study-id="study.currentStudy?.id || null" placeholder="可选" />
+      </el-form-item>
       <el-form-item label="类别" prop="category">
         <el-select v-model="form.category" placeholder="请选择">
           <el-option v-for="c in categories" :key="c" :label="c" :value="c" />
@@ -34,6 +37,7 @@ import type { FormInstance, FormRules } from "element-plus";
 import { ElMessage } from "element-plus";
 import { createIssue, updateIssue } from "../api/issues";
 import { useStudyStore } from "../store/study";
+import SubjectSelect from "./selectors/SubjectSelect.vue";
 
 interface Props {
   modelValue: boolean;
@@ -57,6 +61,7 @@ const levels = ["LOW", "MEDIUM", "HIGH", "CRITICAL"];
 
 const form = reactive({
   title: "",
+  subject_id: "",
   category: "ISSUE",
   level: "MEDIUM",
   due_date: "",
@@ -77,6 +82,7 @@ watch(
     if (val) {
       Object.assign(form, {
         title: val.title || "",
+        subject_id: val.subject_id || "",
         category: val.category || "ISSUE",
         level: val.level || "MEDIUM",
         due_date: val.due_date || "",
@@ -85,6 +91,7 @@ watch(
     } else {
       Object.assign(form, {
         title: "",
+        subject_id: "",
         category: "ISSUE",
         level: "MEDIUM",
         due_date: "",