feat(frontend): integrate self-hosted Inter Google font

Use next/font/google to download and host Inter locally, injecting it into html root via Tailwind CSS variables and fallback to PingFang SC for Chinese characters.

frontend/app/layout.tsx

@@ -1,4 +1,5 @@
 import type {Metadata} from "next";
+import {Inter} from "next/font/google";
 import {Toaster} from "@/components/ui/sonner";
 import {ThemeProvider} from "@/components/layout/theme-provider";
 import {CustomThemeProvider} from "@/lib/theme";
@@ -10,6 +11,12 @@ import {SiteTitleUpdater} from "@/components/providers/title-updater";
 import {RobotsMeta} from "@/components/layout/robots-meta";
 import "./globals.css";
 
+const inter = Inter({
+  subsets: ["latin"],
+  variable: "--font-inter",
+  display: "swap",
+});
+
 export const metadata: Metadata = {
   title: "Wavelet Platform",
   description: "通用二次开发标准范式平台",
@@ -23,7 +30,7 @@ export default function RootLayout({
   return (
     <html
       lang="zh-CN"
-      className="hide-scrollbar font-sans"
+      className={`hide-scrollbar font-sans ${inter.variable}`}
       suppressHydrationWarning
     >
       <body