fix: refine landing and auth entry design

frontend/components/landing/InstitutionalLandingPage.tsx

@@ -249,8 +249,11 @@ function InstitutionalLandingScreen({ locale }: { locale: LandingLocale }) {
       <LandingAnalytics />
       <header className="sticky top-0 z-30 border-b border-slate-200 bg-[#fbfbfa]/90 backdrop-blur-xl">
         <div className="mx-auto flex h-14 max-w-6xl items-center justify-between px-4 sm:px-6">
-          <Link href="/" className="flex items-center gap-2 transition-opacity hover:opacity-80">
-            <img src="/logo.png" alt="PolyWeather" className="h-7 w-auto object-contain" />
+          <Link
+            href="/"
+            className="text-base font-black tracking-tight text-slate-950 transition-opacity hover:opacity-80 sm:text-lg"
+          >
+            PolyWeather
           </Link>
 
           <nav className="hidden items-center gap-7 text-sm font-medium text-slate-500 md:flex">

frontend/components/landing/__tests__/landingPricingReferral.test.ts

@@ -49,6 +49,12 @@ export function runTests() {
   assert(!source.includes("高频刷新与 API 仍为 Pro 权益"), "landing page must not incorrectly exclude high-frequency refresh or API from trial access");
   assert(source.includes("bg-[#fbfbfa]"), "landing page must use a light Notion-style background");
   assert(source.includes("WeatherWorkflowIllustration"), "landing page must include a friendly illustration surface");
+  assert(
+    /className="text-base font-black tracking-tight text-slate-950[\s\S]*?>\s*PolyWeather\s*<\/Link>/.test(
+      source,
+    ),
+    "landing header must expose a readable PolyWeather wordmark instead of a tiny square logo image",
+  );
   assert(!fs.existsSync(publicPngPath), "heavy PNG preview must not remain in public static assets");
   assert(fs.existsSync(fixturePngPath), "PNG preview may only remain as a test fixture");
   assert(fs.existsSync(webpPath), "landing page must ship a WebP preview image for the LCP product screenshot");