UI: unified design system, light/dark themes, redesigned pages and player UI

Tokens and components in styles.css, shared Ui (dialogs, toasts), icons,
bottom tab bar on mobile, keyboard/gamepad navigation, library shelf with
filters and conversion badges, hero game page, restyled player screens.
Games list now returns per-game version counts. Adds docs/UI_DESIGN.md.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

backend/app/schemas.py

@@ -90,6 +90,10 @@ class GameOut(ORM):
     engine: str
     cover_hash: str | None
     created_at: datetime
+    # version counts visible to the requesting user (filled by the list endpoint)
+    ready_versions: int = 0
+    pending_versions: int = 0
+    failed_versions: int = 0
 
 
 class GameDetailOut(GameOut):