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/api/page.tsx

@@ -0,0 +1,17 @@
+import {LegalPageLayout} from "@/components/common/docs/legal-page-layout";
+import {apiSections, DOCS_LAST_UPDATED} from "@/components/common/docs/api";
+
+export default function ApiDocPage() {
+  return (
+    <LegalPageLayout
+      title="API 接口文档"
+      lastUpdated={DOCS_LAST_UPDATED}
+      sections={apiSections}
+      description={
+        <p className="text-muted-foreground text-sm leading-relaxed">
+          OpenFlare 提供简单、强大的 API 接口，支持多种编程语言和开发环境。通过标准化的 RESTful 接口，您可以轻松地与后端服务进行集成与二次开发。
+        </p>
+      }
+    />
+  );
+}