Build ai4ai-survey.github.io as a short English page, not a copy (#25)

The second domain now serves an English-only "What is AI4AI?" read built from the article: its own definition of the field, one takeaway per section, the figures, the closure table and the conclusion, linking to the full article for the rest.

Author: Andyyesiyu

ai4ai/index.html

@@ -360,8 +360,8 @@ <h1>AI4AI Survey: From Long-Horizon Agents to Recursive Self-Improvement</h1>
             <b aria-hidden="true">↗</b>
           </a>
           <a class="project-page-link" href="https://ai4ai-survey.github.io/" target="_blank" rel="noreferrer">
-            <span class="lang-en" lang="en">Project page</span>
-            <span class="lang-zh" lang="zh-CN">项目主页</span>
+            <span class="lang-en" lang="en">Short version (English)</span>
+            <span class="lang-zh" lang="zh-CN">英文短版</span>
             <b aria-hidden="true">↗</b>
           </a>
         </div>

assets/styles.css

@@ -371,6 +371,10 @@ footer a:hover { color: var(--fg); }
 .project-page .glance ol { margin: 0 0 0 1.25rem; }
 .project-page .glance li { margin-bottom: .55rem; color: var(--soft); font-size: 15px; line-height: 1.55; }
 .project-page .glance li a { color: var(--fg); font-weight: 600; }
+/* "Read this section in full" links on the short version of the survey. */
+.project-page .full-link { margin: -.6rem 0 1.8rem; font: 500 14px/1.4 var(--sans); }
+.project-page .full-link a { color: var(--soft); }
+.project-page .full-link a:hover { color: var(--fg); }
 
 /* Wide viewports get a sticky contents rail in the left gutter while the article
    column stays centered. Below 1200px there is no room, so the rail is dropped. */