Polish + Optimize: Clean metadata, remove !important, prune unused CSS

- Update theme-color to match brand (#f8fafc), fix stale CRA description
- Remove manifest.json and logo192.png references (not used)
- Replace !important on chart export buttons with higher specificity selectors
- Remove unused .skeleton-text and .skeleton-loading CSS classes
- Remove duplicate skeleton animation keyframes

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

index.html

@@ -4,13 +4,8 @@
     <meta charset="utf-8" />
     <link rel="icon" href="/favicon.ico" />
     <meta name="viewport" content="width=device-width, initial-scale=1" />
-    <meta name="theme-color" content="#000000" />
-    <meta
-      name="description"
-      content="Web site created using create-react-app"
-    />
-    <link rel="apple-touch-icon" href="/logo192.png" />
-    <link rel="manifest" href="/manifest.json" />
+    <meta name="theme-color" content="#f8fafc" />
+    <meta name="description" content="HiHala Data Dashboard — Museum analytics, visitor tracking, and revenue insights" />
     <link rel="preconnect" href="https://fonts.googleapis.com">
     <link rel="preconnect" href="https://fonts.gstatic.com" crossorigin>
     <link href="https://fonts.googleapis.com/css2?family=DM+Sans:wght@400;500;600&family=IBM+Plex+Sans+Arabic:wght@400;500;600;700&display=swap" rel="stylesheet">