Review fixes #2: bigger flag star, TG header below nav, board-tile relocation

Addressing the review on #23:
- Flag star scaled up ~25% (the hammer&sickle emblem unchanged, kept clear of it).
- TG fullscreen header: drop the WHOLE header below the content-safe-area top
  inset (the hamburger stays to the right of the title), instead of pinning the
  hamburger to the physical top edge.
- DnD: a placed (pending) tile can now be relocated by dragging it to another
  board cell (board->board); it lifts off its source cell while dragged; and it
  can be grabbed even on the zoomed board (touch-action:none on the pending
  cell, so the drag wins over the board pan). The manual-selection blue frame
  now clears on recall.

ui/src/components/Header.svelte

@@ -96,13 +96,4 @@
   :global(html.tg-fullscreen) .bar {
     padding-top: var(--tg-content-top);
   }
-  :global(html.tg-fullscreen) .end {
-    position: fixed;
-    top: 0;
-    left: 50%;
-    transform: translateX(-50%);
-    height: var(--tg-content-top);
-    justify-content: center;
-    z-index: 30;
-  }
 </style>