center all panel titles on phones

src/app/web.css

@@ -1095,6 +1095,12 @@ html[data-theme="web"][data-scheme="dark"] .heatmap-legend-cell[data-level="4"]
   .web-tile-note {
     text-align: center;
   }
+  /* Finish the job: center every panel title (with its eyebrow) and the
+     quick-tile titles too. */
+  .web-section-head,
+  .web-tile-title {
+    text-align: center;
+  }
   /* Section nav: fit every link on screen instead of a sideways-scrolling row,
      so the collapsed top panel never scrolls horizontally — a 3-up button
      grid (2-up on very narrow phones, see the 374px block below) styled like