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/PackDrawCardWeightEntry.cs

@@ -0,0 +1,24 @@
+using System.ComponentModel.DataAnnotations.Schema;
+using SVSim.Database.Common;
+using SVSim.Database.Enums;
+
+namespace SVSim.Database.Models;
+
+/// <summary>
+/// Per-card-rate fact: which card prints in which (pack, slot, tier) at what rate.
+/// RatePct is nullable for rate-less "Guaranteed Leader Card" rows (sampler uses
+/// "uniform over (pool minus owned)" in that case).
+/// </summary>
+public class PackDrawCardWeightEntry : BaseEntity<long>
+{
+    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
+    public override long Id { get; set; }
+
+    public int PackId { get; set; }
+    public DrawSlot Slot { get; set; }
+    public DrawTier Tier { get; set; }
+    public long CardId { get; set; }
+    public double? RatePct { get; set; }
+    public bool IsLeader { get; set; }
+    public bool IsAltArt { get; set; }
+}