Game share-loop: instrument funnel, deep-link shares, /play metadata

Sharpen the existing daily-game share loop into something measurable (per Codex's
"instrument what you have, then feed people into it" plan), ahead of a Show HN launch.

Analytics:
- Per-game funnel events <game>_{arrival,started,completed,shared} (article_id=0).
  arrival = landed via a shared link (utm_source=game_share); started = first move
  (guess/find/flip); completed = solved/cleared/Full Bloom; shared = on share success.
- trackVisit() moved into the global layout so direct /play landings count; the
  server-rendered /a/ share page now creates a visitor token + sends a daily visit
  beacon (first-time /a/-only visitors were previously dropped).
- Admin "Games funnel" panel: arrivals / engaged / completed / shared, per game.

Sharing:
- Memory Match gains a Share button (it was the only game without one).
- All shares deep-link to the exact game+variant with a full https:// URL +
  utm_source=game_share (gameShareUrl helper), instead of a bare /play.
- "shared" is counted only after navigator.share()/clipboard.writeText() succeeds.

/play social metadata:
- /play served homepage canonical/OG (static SPA, ssr=false). postbuild script
  patches build/play.html's head to /play canonical/title/description/OG; fails the
  build if the homepage tags drift. Caddy try_files now serves {path}.html so /play
  is served from the patched file (snapshot in deploy/caddy/).

Tests: backend 352, frontend 27.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/routes/+layout.svelte

@@ -3,10 +3,16 @@
   import { onMount } from 'svelte';
   import FeedbackModal from '$lib/components/FeedbackModal.svelte';
   import { fb, openFeedback, closeFeedback } from '$lib/feedback.svelte.js';
+  import { trackVisit } from '$lib/analytics.js';
   let { children } = $props();
   // Tell the boot-failure seatbelt (app.html) the app mounted — clears the
   // recovery card + timeout as soon as the shell hydrates.
-  onMount(() => window.__ubBooted?.());
+  onMount(() => {
+    window.__ubBooted?.();
+    // Count the daily visit at the LAYOUT level so every landing page counts —
+    // direct /play and /a/ arrivals included, not just the news homepage.
+    trackVisit();
+  });
 </script>
 
 {@render children()}