refactor(repo): consolidate openflare-server to root and move subprojects to internal/apps

- Merge all files inside openflare-server to the repository root directory.
- Relocate agent, relay, and flared subprojects from internal/ to internal/apps/.
- Combine docker-compose files and update build context paths to root.
- Update GitHub workflows and Dockerfiles to refer to new directories and package names.
- Rewrite Go package imports across all files.
- Resolve database renew test race condition and clean up docs.

frontend/lib/theme/index.ts

@@ -0,0 +1,19 @@
+/**
+ * 主题系统
+ * 统一导出整个主题系统的所有功能
+ */
+
+/* 类型定义 */
+export type { Theme, ThemeColors, ThemeConfig } from "./types"
+
+/* 配置 */
+export { THEME_CONFIG } from "./config"
+
+/* 服务端工具 */
+export { getAvailableThemes } from "./parser"
+
+/* 客户端工具 */
+export { getStoredThemeId, setStoredThemeId, removeStoredThemeId } from "./storage"
+
+/* React 上下文和 Hooks */
+export { CustomThemeProvider, useCustomTheme } from "./context"