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/api/languages.ts

@@ -0,0 +1,36 @@
+import client from './client';
+
+// --- Types ---
+
+export interface LanguageInfo {
+  code: string;
+  name: string;
+  enabled: boolean;
+  translations?: Record<string, string>;
+}
+
+export interface UpdateLanguageRequest {
+  name?: string;
+  enabled?: boolean;
+  translations?: Record<string, string>;
+}
+
+// --- API Functions ---
+
+export async function listLanguages(): Promise<LanguageInfo[]> {
+  const { data } = await client.get<{ success: boolean; data: LanguageInfo[] }>(
+    '/config/languages',
+  );
+  return data.data;
+}
+
+export async function updateLanguage(
+  code: string,
+  req: UpdateLanguageRequest,
+): Promise<LanguageInfo> {
+  const { data } = await client.put<{ success: boolean; data: LanguageInfo }>(
+    `/config/languages/${code}`,
+    req,
+  );
+  return data.data;
+}