feat(student): 实现学生的新增与删除功能

- 新增AddStudentReqVO和DeleteStudentReqVO请求对象
- 在StudentController中添加新增和删除学生接口
- StudentService及其实现类增加新增和删除学生方法
- 通过StudentDOMapper新增插入和逻辑删除方法
- 新增AddStudentDialog组件，实现学生添加的表单及交互
- 在class.vue页面添加新增学生按钮及删除学生操作列
- API层新增addStudent和deleteStudent接口调用
- 删除学生时更新选中状态及重新加载学生列表
- 初始化新增学生时词汇掌握记录相关数据

enlish-vue/src/layouts/components/AddStudentDialog.vue

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+<template>
+	<el-dialog v-model="visible" title="新增学生" width="560px" :close-on-click-modal="false">
+		<div class="space-y-4" v-loading="loading">
+			<el-form label-width="90px">
+				<el-form-item label="姓名">
+					<el-input v-model="name" placeholder="请输入学生姓名" clearable />
+				</el-form-item>
+				<el-form-item label="年级">
+					<el-select v-model="gradeId" placeholder="请选择年级" style="width: 260px" @change="handleGradeChange">
+						<el-option v-for="g in gradeOptions" :key="g.id" :label="g.title" :value="g.id" />
+					</el-select>
+				</el-form-item>
+				<el-form-item label="班级">
+					<el-select v-model="classId" placeholder="请选择班级" style="width: 260px">
+						<el-option v-for="c in filteredClassOptions" :key="c.id" :label="c.title" :value="c.id" />
+					</el-select>
+					<div v-if="gradeId && filteredClassOptions.length === 0" class="mt-2 flex items-center gap-2">
+						<span class="text-xs text-gray-500">当前年级暂无班级</span>
+						<el-button type="primary" size="small" @click="showAddClassDialog = true">新增班级</el-button>
+					</div>
+				</el-form-item>
+				<el-form-item label="入学时间">
+					<el-date-picker v-model="startDate" type="datetime" placeholder="选择日期时间"
+						format="YYYY-MM-DD HH:mm:ss" value-format="YYYY-MM-DD HH:mm:ss" />
+				</el-form-item>
+			</el-form>
+		</div>
+		<template #footer>
+			<div class="flex justify-end gap-2">
+				<el-button @click="visible = false">取消</el-button>
+				<el-button type="primary" :disabled="!canSubmit" @click="handleSubmit">确定</el-button>
+			</div>
+		</template>
+	</el-dialog>
+	<AddClassDialog v-model="showAddClassDialog" :default-grade-id="gradeId" @success="onAddClassSuccess" />
+</template>
+
+<script setup>
+import { ref, computed, watch } from 'vue'
+import { getGradeList } from '@/api/grade'
+import { getClassList } from '@/api/class'
+import { addStudent } from '@/api/student'
+import AddClassDialog from '@/layouts/components/AddClassDialog.vue'
+
+const props = defineProps({
+	modelValue: { type: Boolean, default: false },
+	defaultClassId: { type: [Number, String], default: null },
+	defaultGradeId: { type: [Number, String], default: null }
+})
+const emit = defineEmits(['update:modelValue', 'success'])
+
+const visible = computed({
+	get: () => props.modelValue,
+	set: (val) => emit('update:modelValue', val)
+})
+
+const loading = ref(false)
+const name = ref('')
+const gradeId = ref(null)
+const classId = ref(null)
+const startDate = ref('')
+const gradeOptions = ref([])
+const classOptions = ref([])
+
+const filteredClassOptions = computed(() => {
+	if (!gradeId.value) return []
+	return classOptions.value.filter(c => String(c.gradeId) === String(gradeId.value))
+})
+const showAddClassDialog = ref(false)
+function onAddClassSuccess() {
+	fetchBaseOptions().then(() => {
+		handleGradeChange()
+	})
+}
+
+const canSubmit = computed(() =>
+	name.value.trim().length > 0 &&
+	!!gradeId.value &&
+	!!classId.value &&
+	!!startDate.value
+)
+
+async function fetchBaseOptions() {
+	loading.value = true
+	try {
+		const [gr, cl] = await Promise.all([
+			getGradeList(1, 100),
+			getClassList(1, 100)
+		])
+		const gd = gr?.data
+		const cd = cl?.data
+		gradeOptions.value = Array.isArray(gd?.data) ? gd.data : []
+		classOptions.value = Array.isArray(cd?.data) ? cd.data : []
+	} finally {
+		loading.value = false
+	}
+}
+
+function handleGradeChange() {
+	if (classId.value) {
+		const match = filteredClassOptions.value.some(c => String(c.id) === String(classId.value))
+		if (!match) classId.value = null
+	}
+}
+
+async function handleSubmit() {
+	if (!canSubmit.value) return
+	loading.value = true
+	try {
+		await addStudent(name.value.trim(), Number(classId.value), Number(gradeId.value), startDate.value)
+		ElMessage.success('新增学生成功')
+		emit('success')
+		visible.value = false
+	} finally {
+		loading.value = false
+	}
+}
+
+watch(
+	() => props.modelValue,
+	async (v) => {
+		if (v) {
+			name.value = ''
+			gradeId.value = props.defaultGradeId ? Number(props.defaultGradeId) : null
+			classId.value = props.defaultClassId ? Number(props.defaultClassId) : null
+			startDate.value = ''
+			await fetchBaseOptions()
+			if (gradeId.value) handleGradeChange()
+		}
+	}
+)
+</script>
+
+<style scoped></style>