fix(ui): suppress tap-flash directly on the header title and back

The global -webkit-tap-highlight-color on #app was not enough on Android
in-app WebViews (Telegram, VK): they only suppress the selection-like tap
flash when -webkit-user-select / -webkit-tap-highlight-color /
-webkit-touch-callout sit DIRECTLY on the tapped element, not inherited.
Set them on the two tappable header controls — the title (a 10-tap debug
target) and the back chevron.

ui/src/components/Header.svelte

@@ -124,6 +124,17 @@
   .back:hover {
     background: var(--surface-2);
   }
+  /* Android in-app WebViews (Telegram, VK) flash a selection-like box on the two tappable header
+     controls — the title (a 10-tap debug target) and the back chevron — on a plain tap. The global
+     -webkit-user-select / -webkit-tap-highlight-color on #app is inherited, but those WebViews only
+     suppress the artifact when the properties sit DIRECTLY on the tapped element. */
+  h1,
+  .back {
+    -webkit-user-select: none;
+    user-select: none;
+    -webkit-touch-callout: none;
+    -webkit-tap-highlight-color: transparent;
+  }
   /* A thin, compact "<" drawn from two borders — lighter than a glyph. */
   .chev {
     width: 11px;