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/app/(docs)/docs/how-to-use/page.tsx

@@ -0,0 +1,18 @@
+import {LegalPageLayout} from "@/components/common/docs/legal-page-layout";
+import {howToUseSections} from "@/components/common/docs/how-to-use";
+import {DOCS_LAST_UPDATED} from "@/components/common/docs/api";
+
+export default function HowToUsePage() {
+  return (
+    <LegalPageLayout
+      title="平台使用指南"
+      lastUpdated={DOCS_LAST_UPDATED}
+      sections={howToUseSections}
+      description={
+        <p className="text-muted-foreground text-sm leading-relaxed">
+          欢迎使用 OpenFlare 管理平台。本文档将引导您快速了解平台的核心组件、角色权限设计及二次开发流程，帮助您快速上手开发。
+        </p>
+      }
+    />
+  );
+}