feat(message): add message center module (Phase 5)

Implement the complete message center with:
- Database migrations for message_templates, messages, message_subscriptions tables
- erp-message crate with entities, DTOs, services, handlers
- Message CRUD, send, read/unread tracking, soft delete
- Template management with variable interpolation
- Subscription preferences with DND support
- Frontend: messages page, notification panel, unread count badge
- Server integration with module registration and routing

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

apps/web/src/pages/messages/MessageTemplates.tsx

@@ -0,0 +1,117 @@
+import { useEffect, useState } from 'react';
+import { Table, Button, Modal, Form, Input, Select, message } from 'antd';
+import type { ColumnsType } from 'antd/es/table';
+import { listTemplates, createTemplate, type MessageTemplateInfo } from '../../api/messageTemplates';
+
+export default function MessageTemplates() {
+  const [data, setData] = useState<MessageTemplateInfo[]>([]);
+  const [total, setTotal] = useState(0);
+  const [page, setPage] = useState(1);
+  const [loading, setLoading] = useState(false);
+  const [modalOpen, setModalOpen] = useState(false);
+  const [form] = Form.useForm();
+
+  const fetchData = async (p = page) => {
+    setLoading(true);
+    try {
+      const result = await listTemplates(p, 20);
+      setData(result.data);
+      setTotal(result.total);
+    } catch {
+      message.error('加载模板列表失败');
+    } finally {
+      setLoading(false);
+    }
+  };
+
+  useEffect(() => {
+    fetchData(1);
+  // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, []);
+
+  const handleCreate = async () => {
+    try {
+      const values = await form.validateFields();
+      await createTemplate(values);
+      message.success('模板创建成功');
+      setModalOpen(false);
+      form.resetFields();
+      fetchData();
+    } catch {
+      message.error('创建失败');
+    }
+  };
+
+  const columns: ColumnsType<MessageTemplateInfo> = [
+    { title: '名称', dataIndex: 'name', key: 'name' },
+    { title: '编码', dataIndex: 'code', key: 'code' },
+    {
+      title: '通道',
+      dataIndex: 'channel',
+      key: 'channel',
+      render: (c: string) => {
+        const map: Record<string, string> = { in_app: '站内', email: '邮件', sms: '短信', wechat: '微信' };
+        return map[c] || c;
+      },
+    },
+    { title: '标题模板', dataIndex: 'title_template', key: 'title_template', ellipsis: true },
+    { title: '语言', dataIndex: 'language', key: 'language', width: 80 },
+    { title: '创建时间', dataIndex: 'created_at', key: 'created_at', width: 180 },
+  ];
+
+  return (
+    <div>
+      <div style={{ marginBottom: 16 }}>
+        <Button type="primary" onClick={() => setModalOpen(true)}>新建模板</Button>
+      </div>
+      <Table
+        columns={columns}
+        dataSource={data}
+        rowKey="id"
+        loading={loading}
+        pagination={{
+          current: page,
+          total,
+          pageSize: 20,
+          onChange: (p) => { setPage(p); fetchData(p); },
+        }}
+      />
+
+      <Modal
+        title="新建消息模板"
+        open={modalOpen}
+        onOk={handleCreate}
+        onCancel={() => { setModalOpen(false); form.resetFields(); }}
+      >
+        <Form form={form} layout="vertical">
+          <Form.Item name="name" label="名称" rules={[{ required: true, message: '请输入名称' }]}>
+            <Input />
+          </Form.Item>
+          <Form.Item name="code" label="编码" rules={[{ required: true, message: '请输入编码' }]}>
+            <Input />
+          </Form.Item>
+          <Form.Item name="channel" label="通道" initialValue="in_app">
+            <Select options={[
+              { value: 'in_app', label: '站内' },
+              { value: 'email', label: '邮件' },
+              { value: 'sms', label: '短信' },
+              { value: 'wechat', label: '微信' },
+            ]} />
+          </Form.Item>
+          <Form.Item name="title_template" label="标题模板" rules={[{ required: true, message: '请输入标题模板' }]}>
+            <Input placeholder="支持 {{variable}} 变量插值" />
+          </Form.Item>
+          <Form.Item name="body_template" label="内容模板" rules={[{ required: true, message: '请输入内容模板' }]}>
+            <Input.TextArea rows={4} placeholder="支持 {{variable}} 变量插值" />
+          </Form.Item>
+          <Form.Item name="language" label="语言" initialValue="zh-CN">
+            <Select options={[
+              { value: 'zh-CN', label: '中文' },
+              { value: 'en-US', label: '英文' },
+            ]} />
+          </Form.Item>
+        </Form>
+      </Modal>
+    </div>
+  );
+}