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/game/Rack.svelte

@@ -83,7 +83,12 @@
   }
   .tile {
     position: relative;
-    flex: 0 0 auto;
+    /* Sit at the natural tile width, but shrink to fit when the row is crowded so a full
+       rack never overflows its wrapper onto the MakeMove control to its right (the confirm
+       button stays pinned at the right screen edge). flex-grow stays 0 so a sparse rack does
+       not stretch its tiles. */
+    flex: 0 1 auto;
+    min-width: 0;
     width: min(12.5vw, 46px);
     aspect-ratio: 1;
     background: var(--tile-bg);