feat(ui): batch of UI polish tweaks

- admin dashboard "Users" count excludes robots (CountUsers, humans only)
- lobby finished-game delete reveal: background matches header/tab-bar (--bg-elev)
- mobile: swipe up on the zoom-out board (no staged tiles) shuffles the rack
- lobby: status icons -25%, game-row top/bottom padding halved
- toast: info tier drifts up ~a tab-bar height while fading over 2s and dismisses
  on tap; error tier unchanged
- game: confirm-move button stays pinned at the right edge; rack tiles shrink to
  fit so a full rack never overflows onto it
- telegram: a successful invite-link redeem shows a welcome window pointing at the bot
- settings: remove the grid-lines toggle; the board is always a gapless checkerboard
- settings/comms hubs: the selected tab highlight wraps icon + label as a pill

Docs: UI_DESIGN (toast, board surface, selected tab), PLAN; e2e updated for the
removed grid-lines toggle.

ui/src/screens/Lobby.svelte

@@ -380,8 +380,8 @@
     align-items: center;
     justify-content: center;
     border: none;
-    background: var(--danger);
-    color: #fff;
+    background: var(--bg-elev);
+    color: var(--text);
     font-size: 1.1rem;
   }
   .row {
@@ -404,7 +404,7 @@
     gap: 12px;
     min-width: 0;
     text-align: left;
-    padding: 10px 6px;
+    padding: 5px 6px;
     border: none;
     background: none;
     color: var(--text);
@@ -471,7 +471,7 @@
     color: var(--text-muted);
   }
   .emoji {
-    font-size: 1.8rem;
+    font-size: 1.35rem;
     line-height: 1;
     flex: 0 0 auto;
   }