Rating Volatility System is Dormant (Wrong Time Scale)

Description
The Glicko-2 system is initialized with a RatingPeriod of 86400 seconds (1 Day). Glicko-2 is designed to update rating deviation (RD) based on "periods" passed. If matches happen frequently (e.g., minutes apart), the calculated periods will be ~0.001. This causes the Volatility update step to be negligible.

How to Reproduce
1. Play 10 matches in one hour.
2. Observe that the RD (Rating Deviation) barely changes or decays slower than expected, making the rating "sticky" and resistant to change even if performance changes drastically.

Root Cause
In glicko2.go:
defaultRatingPeriodSec = 86400 // 1 day
And rating_service.go initializes with nil config, using this default.

Expected Behavior
The rating period should match the platform's expected usage frequency so that rating confidence (RD) updates dynamically.