feat(CS): weekly auto-schedule (day-of-week + UTC time), persisted, /csschedule GM cmd

The siege can now auto-open registration on scheduled days/time instead of only
manual /csphase. Schedule is context-owned state (like owner), persisted across
restarts via the same config-JSON path. New GM command /csschedule sets/views/clears
it (e.g. /csschedule Sunday 20:00, UTC). +2 unit tests (11 total).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/GameLogic/PlugIns/PeriodicTasks/CastleSiegeEventPlugIn.cs

@@ -75,7 +75,7 @@ public sealed class CastleSiegeEventPlugIn : IPeriodicTaskPlugIn, ISupportCustom
 
             // Restore state persisted before the last restart (owner/phase/registrations) BEFORE subscribing,
             // so restoring doesn't announce phases or re-spawn defenses.
-            created.RestoreState(config.PersistedOwnerGuildName, config.PersistedPhase, config.PersistedPhaseStartedUtc, config.PersistedRegisteredGuilds);
+            created.RestoreState(config.PersistedOwnerGuildName, config.PersistedPhase, config.PersistedPhaseStartedUtc, config.PersistedRegisteredGuilds, config.PersistedScheduleDays, config.PersistedScheduleTime);
 
             // Announce phase changes to the whole server and, when the siege begins, warp registered members.
             created.PhaseChanged += phase => _ = OnPhaseChangedAsync(gc, created, phase);
@@ -150,6 +150,8 @@ public sealed class CastleSiegeEventPlugIn : IPeriodicTaskPlugIn, ISupportCustom
             config.PersistedPhase = context.Phase;
             config.PersistedPhaseStartedUtc = context.PhaseStartedUtc;
             config.PersistedRegisteredGuilds = context.RegisteredGuilds.ToList();
+            config.PersistedScheduleDays = context.ScheduleDays.ToList();
+            config.PersistedScheduleTime = context.ScheduleTime;
 
             // Find our plugin-configuration row via the in-memory config graph to get its id.
             var pluginTypeId = typeof(CastleSiegeEventPlugIn).GUID;