feat(game-detail): link sections to filtered lists (#66)

Add "View all" links to the Purchases / Sessions / Play Events sections
on the game-detail page, each pointing at the matching filtered list view
via filter_url(). Pure consumer of the #56 filter_url()/where() helpers;
no new filter machinery.

- _game_section() gains an optional view_all_url, rendered as a gray xs
  button beside the heading (shown only when the section is non-empty).
- New arrowright icon for the link.
- Tests: each section renders the expected escaped href; a parity test
  asserts each link's filter scopes to the game and excludes others.

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

games/templates/icons/arrowright.html

@@ -0,0 +1,3 @@
+<svg class="dark:text-white w-3" viewBox="5 5 14 14" fill="none" xmlns="http://www.w3.org/2000/svg">
+    <path d="M9 6L15 12L9 18" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"/>
+</svg>