feat(web): refresh palette, simplify ranking toolbar and drop export

reaction_board/web/static/index.html

@@ -4,6 +4,8 @@
   <meta charset="utf-8">
   <meta name="viewport" content="width=device-width, initial-scale=1, viewport-fit=cover">
   <meta name="color-scheme" content="light dark">
+  <meta name="theme-color" content="#f7f2ea" media="(prefers-color-scheme: light)">
+  <meta name="theme-color" content="#1b1411" media="(prefers-color-scheme: dark)">
   <title>咻咻满 Reaction 看板</title>
   <link rel="icon" href="/static/favicon.svg" type="image/svg+xml">
   <link rel="stylesheet" href="/static/style.css">
@@ -18,9 +20,9 @@
           <small id="topbar-title">最新动态</small>
         </span>
       </a>
-      <span class="topbar-hint">只读</span>
+      <span class="topbar-hint" id="topbar-hint" hidden>预览</span>
     </header>
-    <div class="preview-banner" id="preview-banner" hidden>预览数据 · 只读 · 不影响真实数据库</div>
+    <div class="preview-banner" id="preview-banner" hidden>预览数据 · 不影响真实数据库</div>
     <main class="main-shell">
       <div id="view"></div>
     </main>