Stage 17 (contour round 3): Telegram Mini Apps polish, board scroll, keyboard overlay

- Telegram (lib/telegram.ts): chrome colours (setHeaderColor/setBackgroundColor/setBottomBarColor) match Telegram's header/bg/bottom bar to the app; native BackButton on sub-screens (app chevron hidden in TG); HapticFeedback on tile place/commit/error; enableClosingConfirmation while a game is open; disableVerticalSwipes so swipe-to-minimise doesn't fight tile drag / board scroll
- #9 board-only vertical scroll: Screen 'column' mode lets the board area scroll while score/status/rack/tab bar stay fixed (zoom keeps its own scroll)
- #10 check-word dialog opens in Modal keyboard-overlay mode (top-anchored, keyboard overlays the empty area) — no resize/relayout jank; other modals stay keyboard-aware
- docs: UI_DESIGN Telegram integration + vertical fit/keyboard; PLAN round 2-3 follow-ups

ui/src/components/Screen.svelte

@@ -14,6 +14,7 @@
     children,
     scroll = true,
     growNav = false,
+    column = false,
   }: {
     title: string;
     back?: string;
@@ -22,13 +23,16 @@
     children?: Snippet;
     scroll?: boolean;
     growNav?: boolean;
+    // column lays the content out as a flex column so a child can own the vertical fit
+    // (the game makes only its board scroll while the score/rack/tab bar stay put).
+    column?: boolean;
   } = $props();
 </script>
 
 <div class="screen">
   <Header {title} {back} {menu} grow={growNav} />
   <AdBanner />
-  <main class="content" class:scroll class:fill={!growNav}>{@render children?.()}</main>
+  <main class="content" class:scroll class:fill={!growNav} class:column>{@render children?.()}</main>
   {#if tabbar}
     <nav class="tabbar">{@render tabbar()}</nav>
   {/if}
@@ -50,6 +54,10 @@
   .content.scroll {
     overflow-y: auto;
   }
+  .content.column {
+    display: flex;
+    flex-direction: column;
+  }
   .tabbar {
     flex: 0 0 auto;
   }