docs(sports): type-hint game_update_timestamps to match its sibling

Addresses the last remaining sub-point on the modes.py review thread. The
design finding itself is already handled: the base class documents that it
only reads game_update_timestamps and that a subclass's update() owns writing
"last_seen" (and afl/etc. do, so stale-game eviction works in practice). The
one concrete gap was the missing annotation -- _zero_clock_timestamps is typed
Dict[str, float] while this nested map had none. Now Dict[str, Dict[str, float]].

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KEZK1P1Q1fu5pcuVrkrCFZ

src/base_classes/sports/modes.py

@@ -847,7 +847,7 @@ class SportsLive(SportsCore):
         # feed: {game_id: {"clock": ts, "score": ts, "last_seen": ts}}.
         # Until a subclass writes "last_seen", the staleness branch of
         # _detect_stale_games is inert and only the game-over check applies.
-        self.game_update_timestamps = {}
+        self.game_update_timestamps: Dict[str, Dict[str, float]] = {}
         self.stale_game_timeout = self.mode_config.get("stale_game_timeout", 300)  # 5 minutes default
 
     @abstractmethod