Remove Warp sponsorship and refine endorsement cards (#1953)

Remove the ended Warp sponsorship from multilingual READMEs and landing pages, and restyle the landing-page endorsements as rounded cards.

ja/docs/index.html

@@ -135,10 +135,10 @@
 </section>
 
 <!-- Section: endorsements -->
-<section data-md-color-scheme="slate" data-md-color-primary="grey" class="home-div home-div--black">
+<section data-md-color-scheme="slate" data-md-color-primary="grey" class="home-div">
     <div class="section-content">
         <h3 style="text-align: center; margin: 1em auto;">推薦文</h3>
-        <div class="intro-container" style="margin: 0 auto;">
+        <div class="intro-container endor-container">
             <div class="intro-text endor-text">
                 <p style="margin-bottom: 0;">「わかりやすいデータ構造とアルゴリズムの入門書で、読者を手と頭の両方を使う学びへと導いてくれます。アルゴリズムを初めて学ぶ人に強くおすすめします。」</p>
                 <p style="font-weight: bold;">—— Junhui Deng、清華大学コンピュータ科学科教授</p>
@@ -205,22 +205,6 @@
     </div>
 </section>
 
-<!-- Section: special thanks -->
-<section class="home-div home-div--black" data-md-color-primary="grey" data-md-color-scheme="slate">
-    <div class="section-content">
-        <h3 style="text-align: center; margin: 0 0 2em 0;">
-        謝辞
-        </h3>
-        <a href="https://go.warp.dev/hello-algo">
-            <img src="https://github.com/warpdotdev/brand-assets/raw/main/Github/Sponsor/Warp-Github-LG-02.png"
-                class="device-on-hover intro-image" style="max-width: 30em;" alt="Warp-Github-LG-02" />
-            <div class="text-button" style="margin: 1em auto;">
-                <span>Warp is built for coding with multiple AI agents.</span>
-            </div>
-        </a>
-    </div>
-</section>
-
 <!-- Section: contributors -->
 <section data-md-color-scheme="slate" data-md-color-primary="grey" class="home-div">
     <div class="section-content" style="max-width: 90vw;">