refactor: Context 与 Provider 合并 — 消除 contexts/ 目录，一文件一状态单元

- ThemeContext + useTheme → ThemeProvider.tsx（原 hooks/use-theme.ts 删除）
- AppContext + useAppContext → AppProvider.tsx（原 contexts/app-context.ts 删除）
- SettingsContext + useSettings → SettingsProvider.tsx（原 contexts/settings-context.ts 删除）
- HomeContext + useHomeContext → HomeContent.tsx（原 contexts/home-context.ts 删除）
- 删除空的 contexts/ 目录，20+ 导入路径同步更新
- TypeScript 编译通过（npx tsc --noEmit 零错误）

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/pages/home/components/ModelInputForm.tsx

@@ -25,8 +25,8 @@ import {
 } from '@ant-design/icons';
 import type { UploadFile } from 'antd/es/upload';
 
-import { useHomeContext } from '@/contexts/home-context';
-import { useAppContext } from '@/contexts/app-context';
+import { useHomeContext } from '@/pages/home/HomeContent';
+import { useAppContext } from '@/components/AppProvider';
 import { useSubmitTask } from '@/hooks/use-api';
 import { emit, EVENTS } from '@/utils/event-bus';
 import type { ModelsListResponseBody, TaskInfoItemResponseBody } from '@/services/modules';