feat(packs): add PackDraw* tables and IsEnabled column

Three new EF entities and a migration:
- PackDrawConfigEntry (per-pack: animation rate, has-bonus flag, special-kind label)
- PackDrawSlotRateEntry (pack/slot/tier -> rate, unique index)
- PackDrawCardWeightEntry (per-card-rate facts incl rate-less rows)

DrawSlot {General, Eighth, Bonus} and DrawTier {Bronze, Silver, Gold, Legendary, Special}.
Special collapses leader_card and limited_time_leader (verified mutually exclusive per pack).

IsEnabled column on PackConfigEntry — admin gate for synthesized stubs, distinct from
the wire-mirror IsHide.

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

SVSim.Database/Models/PackConfigEntry.cs

@@ -33,6 +33,13 @@ public class PackConfigEntry : BaseEntity<int>
 
     public int OpenCountLimit { get; set; }
 
+    /// <summary>
+    /// Server admin gate. True for live-capture-derived rows; false for synthesized stubs
+    /// (operator opt-in per pack). Filtered in PackRepository.GetActivePacks; distinct from
+    /// the wire-mirror IsHide.
+    /// </summary>
+    public bool IsEnabled { get; set; } = true;
+
     public PackGachaPointConfig? GachaPointConfig { get; set; }
 
     public List<PackBannerEntry> Banners { get; set; } = new();