feat(stats): link stats rows and counts to filtered lists (#65)

Wire the stats page to filter_url()/stats_links:
- Per-row session links on game superlatives, games-by-playtime, platform
  and month rows (game rows keep their detail GameLink, add a session icon).
- Count links: sessions, games, total/refunded/dropped/unfinished/backlog
  purchases.
- Cap preview lists to 5 with a 'View all (N)' link passing ?sort= for order
  parity; remove the redundant 'All Purchases' list.
- stats_data: carry platform_id for platform links; drop the all-time
  games-by-playtime [:10] slice so the view-all count is honest (rendering
  caps the preview).

Also make the filter bar's _extract_labeled tolerate bare choice/multi values
so a programmatically-built filter URL renders instead of crashing.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RF5L4HtbcykTfY9YUYGds3

games/views/stats_data.py

@@ -247,7 +247,7 @@ def compute_stats(year: int | None = None) -> StatsData:
             .annotate(total_playtime=Sum("sessions__duration_total"))
             .filter(total_playtime__gt=timedelta(0))
         )
-        top_games = games_with_playtime.order_by("-total_playtime")[:10]
+        top_games = games_with_playtime.order_by("-total_playtime")
     else:
         games_with_playtime = (
             Game.objects.filter(sessions__timestamp_start__year=year)
@@ -256,11 +256,16 @@ def compute_stats(year: int | None = None) -> StatsData:
         )
         top_games = games_with_playtime.order_by("-total_playtime")
 
+    # platform_id is carried alongside the name so the stats row can link to a
+    # platform-scoped session list (#65).
     total_playtime_per_platform = (
-        sessions.values("game__platform__name")
+        sessions.values("game__platform__name", "game__platform__id")
         .annotate(playtime=Sum(F("duration_total")))
-        .annotate(platform_name=F("game__platform__name"))
-        .values("platform_name", "playtime")
+        .annotate(
+            platform_name=F("game__platform__name"),
+            platform_id=F("game__platform__id"),
+        )
+        .values("platform_name", "platform_id", "playtime")
         .order_by("-playtime")
     )