fix(telegram): paint the home-indicator strip with the bottom bar's colour

The safe-area bottom inset was reserved on the Screen wrapper, so the strip
that holds space for the home indicator showed the content background and read
as detached from the coloured bottom bar / header above it.

Move the bottom inset onto the bottom bar: the Screen .tabbar wrapper now paints
--bg-elev and pads itself by --tg-safe-bottom, so the strip continues the
TabBar's chrome; a screen with no tab bar pads its bottom-most content
(.content:last-child) instead, so the strip takes that content's own colour.

ui/src/components/Screen.svelte

@@ -101,9 +101,10 @@
        bottom input — chat, word-check — stays above an open soft keyboard without the page
        scrolling; falls back to the full height where the var is unset. */
     height: var(--vvh, 100%);
-    /* Clear the device safe-area cut-outs inside Telegram — the home indicator at the bottom and
-       the notch sides in landscape; all 0 elsewhere. The top inset is owned by the header. */
-    padding-bottom: var(--tg-safe-bottom, 0px);
+    /* Clear the landscape notch sides inside Telegram (0 elsewhere). The top inset is owned by the
+       header; the home-indicator (bottom) inset is owned by the bottom bar — the .tabbar paints its
+       own chrome into it, and a screen with no tab bar pads its content (.content:last-child) — so
+       the strip takes the bar's colour rather than the detached content background. */
     padding-left: var(--tg-safe-left, 0px);
     padding-right: var(--tg-safe-right, 0px);
   }
@@ -121,7 +122,18 @@
     display: flex;
     flex-direction: column;
   }
+  /* No tab bar → the content is the bottom-most element: pad it by the device home-indicator inset
+     so it clears the cut-out, the strip taking the content's own background. With a tab bar the
+     .tabbar owns that inset instead (and content is not the last child, so this does not apply). */
+  .content:last-child {
+    padding-bottom: var(--tg-safe-bottom, 0px);
+  }
   .tabbar {
     flex: 0 0 auto;
+    /* Extend the bottom bar's chrome (the TabBar's --bg-elev) under the device home indicator
+       inside Telegram (the inset is 0 elsewhere), so the safe-area strip reads as part of the bar
+       instead of the content background showing through. */
+    background: var(--bg-elev);
+    padding-bottom: var(--tg-safe-bottom, 0px);
   }
 </style>