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/parser.ts

@@ -0,0 +1,11 @@
+import type {Theme} from "./types"
+import themesData from "./themes.json"
+
+/**
+ * 获取所有可用主题
+ * 从预生成的 themes.json 中直接读取主题列表和颜色配置
+ * @returns 主题列表，已按默认主题优先且其余按名称排序
+ */
+export async function getAvailableThemes(): Promise<Theme[]> {
+  return themesData as Theme[];
+}