style: neutral outlined hero Links buttons

Drop the per-color gradients (blue/teal/amber) on the Paper/Demo/Dashboard
buttons for a quiet surface+border style that follows the theme variables
in both light and dark mode.

app/src/components/Hero.astro

@@ -281,21 +281,21 @@ const pdfFilename = `${slugify(pdfBase)}.pdf`;
   .meta-container .button {
     text-decoration: none;
   }
-  /* Links cell: stack buttons vertically, each its own accent color */
+  /* Links cell: stacked, quiet outlined buttons */
   .hero-links {
     display: flex;
     flex-direction: column;
     align-items: flex-start;
     gap: 6px;
   }
-  .hero-links .button.lk-paper {
-    background: linear-gradient(15deg, #34506f 0%, #3d5a80 35%);
+  .hero-links .button {
+    background: var(--surface-bg);
+    color: var(--text-color);
+    border-color: var(--border-color);
   }
-  .hero-links .button.lk-demo {
-    background: linear-gradient(15deg, #24796e 0%, #2a8f82 35%);
-  }
-  .hero-links .button.lk-dash {
-    background: linear-gradient(15deg, #a86f24 0%, #bf7d2c 35%);
+  .hero-links .button:hover {
+    border-color: var(--muted-color);
+    filter: none;
   }
   .meta-container-cell {
     display: flex;