fix: resolve E2E audit findings and add Phase C frontend pages

- Fix audit_log handler multi-tenant bug: use Extension<TenantContext>
  instead of hardcoded default_tenant_id
- Fix sendMessage route mismatch: frontend /messages/send → /messages
- Add POST /users/{id}/roles backend route for role assignment
- Add task.completed event payload: started_by + instance_id for
  notification delivery
- Add audit log viewer frontend page (AuditLogViewer.tsx)
- Add language management frontend page (LanguageManager.tsx)
- Add api/auditLogs.ts and api/languages.ts modules

apps/web/src/pages/settings/LanguageManager.tsx

@@ -0,0 +1,210 @@
+import { useState, useEffect, useCallback } from 'react';
+import {
+  Table,
+  Switch,
+  Modal,
+  Form,
+  Input,
+  Button,
+  Space,
+  Typography,
+  message,
+  Card,
+} from 'antd';
+import { EditOutlined } from '@ant-design/icons';
+import {
+  listLanguages,
+  updateLanguage,
+  type LanguageInfo,
+} from '../../api/languages';
+
+// --- Component ---
+
+export default function LanguageManager() {
+  const [languages, setLanguages] = useState<LanguageInfo[]>([]);
+  const [loading, setLoading] = useState(false);
+  const [editModalOpen, setEditModalOpen] = useState(false);
+  const [editingLang, setEditingLang] = useState<LanguageInfo | null>(null);
+  const [editForm] = Form.useForm();
+
+  const fetchLanguages = useCallback(async () => {
+    setLoading(true);
+    try {
+      const result = await listLanguages();
+      setLanguages(result);
+    } catch {
+      message.error('加载语言列表失败');
+    }
+    setLoading(false);
+  }, []);
+
+  useEffect(() => {
+    fetchLanguages();
+  }, [fetchLanguages]);
+
+  // --- Enable / Disable Toggle ---
+
+  const handleToggle = async (record: LanguageInfo, enabled: boolean) => {
+    try {
+      await updateLanguage(record.code, { enabled });
+      setLanguages((prev) =>
+        prev.map((lang) =>
+          lang.code === record.code ? { ...lang, enabled } : lang,
+        ),
+      );
+      message.success(enabled ? '已启用' : '已禁用');
+    } catch {
+      message.error('操作失败');
+    }
+  };
+
+  // --- Edit Modal ---
+
+  const openEdit = (lang: LanguageInfo) => {
+    setEditingLang(lang);
+    editForm.setFieldsValue({
+      name: lang.name,
+      translations: lang.translations
+        ? Object.entries(lang.translations)
+            .map(([key, value]) => `${key}=${value}`)
+            .join('\n')
+        : '',
+    });
+    setEditModalOpen(true);
+  };
+
+  const closeEdit = () => {
+    setEditModalOpen(false);
+    setEditingLang(null);
+    editForm.resetFields();
+  };
+
+  const handleEditSubmit = async (values: { name: string; translations: string }) => {
+    if (!editingLang) return;
+
+    const translations: Record<string, string> = {};
+    if (values.translations?.trim()) {
+      for (const line of values.translations.split('\n')) {
+        const trimmed = line.trim();
+        if (!trimmed) continue;
+        const eqIndex = trimmed.indexOf('=');
+        if (eqIndex === -1) continue;
+        const key = trimmed.slice(0, eqIndex).trim();
+        const val = trimmed.slice(eqIndex + 1).trim();
+        if (key) {
+          translations[key] = val;
+        }
+      }
+    }
+
+    try {
+      const updated = await updateLanguage(editingLang.code, {
+        name: values.name,
+        translations,
+      });
+      setLanguages((prev) =>
+        prev.map((lang) =>
+          lang.code === editingLang.code ? updated : lang,
+        ),
+      );
+      message.success('语言更新成功');
+      closeEdit();
+    } catch (err: unknown) {
+      const errorMsg =
+        (err as { response?: { data?: { message?: string } } })?.response?.data
+          ?.message || '更新失败';
+      message.error(errorMsg);
+    }
+  };
+
+  // --- Columns ---
+
+  const columns = [
+    {
+      title: '语言代码',
+      dataIndex: 'code',
+      key: 'code',
+      width: 160,
+    },
+    {
+      title: '语言名称',
+      dataIndex: 'name',
+      key: 'name',
+      width: 200,
+    },
+    {
+      title: '状态',
+      dataIndex: 'enabled',
+      key: 'enabled',
+      width: 120,
+      render: (enabled: boolean, record: LanguageInfo) => (
+        <Switch checked={enabled} onChange={(checked) => handleToggle(record, checked)} />
+      ),
+    },
+    {
+      title: '翻译条目数',
+      key: 'translationCount',
+      width: 140,
+      render: (_: unknown, record: LanguageInfo) =>
+        record.translations ? Object.keys(record.translations).length : 0,
+    },
+    {
+      title: '操作',
+      key: 'actions',
+      render: (_: unknown, record: LanguageInfo) => (
+        <Space>
+          <Button
+            size="small"
+            icon={<EditOutlined />}
+            onClick={() => openEdit(record)}
+          >
+            编辑
+          </Button>
+        </Space>
+      ),
+    },
+  ];
+
+  return (
+    <div>
+      <Typography.Title level={5} style={{ marginBottom: 16 }}>
+        语言管理
+      </Typography.Title>
+
+      <Card>
+        <Table
+          columns={columns}
+          dataSource={languages}
+          rowKey="code"
+          loading={loading}
+          pagination={false}
+        />
+      </Card>
+
+      {/* Edit Modal */}
+      <Modal
+        title={`编辑语言 - ${editingLang?.name ?? ''}`}
+        open={editModalOpen}
+        onCancel={closeEdit}
+        onOk={() => editForm.submit()}
+      >
+        <Form form={editForm} onFinish={handleEditSubmit} layout="vertical">
+          <Form.Item
+            name="name"
+            label="语言名称"
+            rules={[{ required: true, message: '请输入语言名称' }]}
+          >
+            <Input />
+          </Form.Item>
+          <Form.Item
+            name="translations"
+            label="翻译内容"
+            extra="每行一条，格式：key=value"
+          >
+            <Input.TextArea rows={10} placeholder={'common.save=保存\ncommon.cancel=取消'} />
+          </Form.Item>
+        </Form>
+      </Modal>
+    </div>
+  );
+}