feat(packs): add PackDraw seed DTOs and IsEnabled on PackSeed

Three new seed DTOs (PackDrawConfigSeed, PackDrawSlotRateSeed,
PackDrawCardWeightSeed) — slot and tier carried as strings, importer
translates to enum.

PackSeed gains is_enabled (defaults true so existing seeds remain
enabled).

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

SVSim.Bootstrap/Models/Seed/PackDrawConfigSeed.cs

@@ -0,0 +1,12 @@
+using System.Text.Json.Serialization;
+
+namespace SVSim.Bootstrap.Models.Seed;
+
+public sealed class PackDrawConfigSeed
+{
+    [JsonPropertyName("pack_id")] public int PackId { get; set; }
+    [JsonPropertyName("short_code")] public string? ShortCode { get; set; }
+    [JsonPropertyName("animation_rate_pct")] public double AnimationRatePct { get; set; }
+    [JsonPropertyName("has_bonus_slot")] public bool HasBonusSlot { get; set; }
+    [JsonPropertyName("special_kind")] public string? SpecialKind { get; set; }
+}