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/ModelSelector.tsx

@@ -8,7 +8,7 @@ import { Tabs, Spin, Empty, Tag, Typography, Button, Result, message, theme as a
 import { AppstoreOutlined } from '@ant-design/icons';
 
 import { useModelList } from '@/hooks/use-api';
-import { useHomeContext } from '@/contexts/home-context';
+import { useHomeContext } from '@/pages/home/HomeContent';
 import { resolveCategoryLabel, MODEL_CATEGORIES } from '@/services/modules';
 import type { ModelsListResponseBody, ModelCategoryStringEnum } from '@/services/modules';