refactor(calendar): delete JstPeriod, update doc comments

All JstPeriod callsites have moved to IGameCalendarService — delete the
static class and its tests. Updates the doc comments on Viewer.cs
(LastLoginBonusClaimedAt) and ViewerEventCounter.cs to reference the
new UTC / config-driven boundary instead of the old "JST 02:00".

GameConfigurationJsonb config-section snapshot test picks up "GameCalendar".

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

SVSim.Database/Models/Viewer.cs

@@ -35,7 +35,7 @@ public class Viewer : BaseEntity<long>
 
     /// <summary>
     /// UTC instant of the most recent daily-login-bonus claim. Null = never claimed.
-    /// Compared against JST 02:00 day boundary via JstPeriod.DayKey to decide eligibility.
+    /// Compared against the daily reset boundary via IGameCalendarService.ResetReady.
     /// </summary>
     public DateTime? LastLoginBonusClaimedAt { get; set; }
 

SVSim.Database/Models/ViewerEventCounter.cs

@@ -3,7 +3,8 @@ namespace SVSim.Database.Models;
 /// <summary>
 /// Per-viewer "how many times has this happened" counter. Composite PK
 /// (ViewerId, EventKey, Period). Period strings: "all-time", "month:YYYY-MM",
-/// "week:YYYY-W##", "day:YYYY-MM-DD" — all JST-anchored with 02:00 day-boundary.
+/// "week:YYYY-W##", "day:YYYY-MM-DD" — all UTC, with the reset-window boundary
+/// set by <c>GameCalendarConfig.DailyResetUtcHour</c>.
 /// Single source of truth for total_count / done_number on every wire shape.
 /// </summary>
 public class ViewerEventCounter