stop infinite retry loop on rejected Lichess tokens

A gamer's periodic check would get permanently stuck if their stored token
was revoked/expired: our stats API collapsed both "Lichess rejected the
token" (401/403, permanent) and genuine transient errors into the same 502
response, so the bot treated an invalid token exactly like a network blip —
retrying the same window forever at a capped 300s backoff, never advancing
the checkpoint (observed in prod: Dor1zz stuck for 100+ consecutive errors
over 8+ hours, admin alerts firing every 25 failures).

Preserve the distinction that already existed one layer down (lichess_client.py
already tells 401/403 apart from other failures) instead of collapsing it in
stats_service.py: add PuzzleOfPeriodResponse.auth_failed, have main.py return
401 specifically for that case, and have the bot raise a distinct
InvalidTokenError instead of returning None. On InvalidTokenError, the bot now
clears the token for that pair, notifies the user to reconnect via /addtoken,
and continues tracking games normally instead of stalling forever.

LichessWebServices/stats_service.py

@@ -839,6 +839,7 @@ class StatsService:
                 return PuzzleOfPeriodResponse(
                     message="Неверный токен авторизации или доступ запрещен",
                     success=False,
+                    auth_failed=True,
                     period_start=since_ms,
                     period_end=until_ms,
                     max_puzzles=max_puzzles,