fix(vk): friend-code link as ?hash, Android safe-area via bridge insets, landscape home-bar colour

Contour review of the VK Bridge group:

- #6 invite link: VK's documented '#' direct-link payload is eaten by the vk.com SPA before it
  reaches the app, so the friend-code link now carries the payload as a query param
  (vk.com/app<id>?hash=f<code>); the recipient already reads the `hash` query param (vkStartParam).
  (Whether VK forwards the '?' through to the iframe is being confirmed on the contour.)
- #8 Android: the VK mobile webview does not surface the home-bar inset via CSS env() (config
  insets are iOS-only), so subscribe to the bridge insets (VKWebAppUpdateConfig + VKWebAppUpdateInsets)
  and set --tg-safe-* to max(env(), the VK value).
- #8 landscape colour: the home-indicator strip was the (grey) page background because the two-pane
  landscape game has no bottom bar. The left-panel controls bar now paints its own chrome into the
  inset (Screen gains a selfInset flag that drops the shell's detached padding strip), and the
  game-land runs flush to the edge.

Verified: svelte-check, 347 unit, build, bundle-gate; the landscape safe-area painting reproduced in
the mock (controls bar + board reach the edge, strip takes the bar colour). The VK-Bridge / VK launch
behaviours (Android insets, the ?hash forward) need the live contour.

ui/src/components/Screen.svelte

@@ -14,6 +14,7 @@
     scroll = true,
     growNav = false,
     column = false,
+    selfInset = false,
   }: {
     title: string;
     back?: string;
@@ -21,6 +22,10 @@
     children?: Snippet;
     scroll?: boolean;
     growNav?: boolean;
+    // selfInset: the content paints the bottom home-indicator inset itself (a tab-bar-less screen
+    // whose own bottom element owns the strip, e.g. the landscape game's left-panel controls), so
+    // the shell does not add the detached .content padding-bottom below it.
+    selfInset?: 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;
@@ -87,7 +92,7 @@
 
 <div class="screen">
   <Header {title} {back} grow={growNav} />
-  <main class="content" class:scroll class:fill={!growNav} class:column>{@render children?.()}</main>
+  <main class="content" class:scroll class:fill={!growNav} class:column class:selfinset={selfInset}>{@render children?.()}</main>
   {#if tabbar}
     <nav class="tabbar">{@render tabbar()}</nav>
   {/if}
@@ -128,6 +133,11 @@
   .content:last-child {
     padding-bottom: var(--tg-safe-bottom, 0px);
   }
+  /* selfInset: the content's own bottom element paints the home-indicator strip (the landscape
+     game's left-panel controls), so the shell does not add a detached padding strip below it. */
+  .content.selfinset:last-child {
+    padding-bottom: 0;
+  }
   .tabbar {
     flex: 0 0 auto;
     /* Extend the bottom bar's chrome (the TabBar's --bg-elev) under the device home indicator