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/Enums/DrawSlot.cs

@@ -0,0 +1,8 @@
+namespace SVSim.Database.Enums;
+
+public enum DrawSlot
+{
+    General = 0,
+    Eighth = 1,
+    Bonus = 2,
+}

SVSim.Database/Enums/DrawTier.cs

@@ -0,0 +1,16 @@
+namespace SVSim.Database.Enums;
+
+/// <summary>
+/// Per-draw page tier the slot rolls into. Distinct from card-master <see cref="Rarity"/>:
+/// for the four base values they line up, but <c>Special</c> covers the per-pack
+/// "Leader Card" / "Limited-Time Leader" tiers — its cards are typically Rarity.Legendary
+/// with the IsLeader printing flag set.
+/// </summary>
+public enum DrawTier
+{
+    Bronze = 0,
+    Silver = 1,
+    Gold = 2,
+    Legendary = 3,
+    Special = 4,
+}