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/Settings.svelte

@@ -2,7 +2,6 @@
   import {
     app,
     setBoardLabels,
-    setBoardLines,
     setLocalePref,
     setReduceMotion,
     setTheme,
@@ -62,14 +61,6 @@
         </button>
       {/each}
     </div>
-    <label class="row gridlines">
-      <span>{t('settings.boardLines')}</span>
-      <input
-        type="checkbox"
-        checked={app.boardLines}
-        onchange={(e) => setBoardLines(e.currentTarget.checked)}
-      />
-    </label>
   </section>
 
   <section>
@@ -124,7 +115,4 @@
     align-items: center;
     justify-content: space-between;
   }
-  .gridlines {
-    margin-top: 12px;
-  }
 </style>