feat(packs): PackDrawTable aggregate + IPackDrawTableRepository

Aggregate (Config + SlotRates + CardWeights) and a single-pack getter
loaded as one unit per /pack/open. PackOpenService consumes the
aggregate; tests use the production seed (fixture overlay) to validate
shape.

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

SVSim.Database/Repositories/PackDrawTable/PackDrawTableRepository.cs

@@ -0,0 +1,30 @@
+using Microsoft.EntityFrameworkCore;
+
+namespace SVSim.Database.Repositories.PackDrawTables;
+
+public class PackDrawTableRepository : IPackDrawTableRepository
+{
+    private readonly SVSimDbContext _db;
+    public PackDrawTableRepository(SVSimDbContext db) { _db = db; }
+
+    public async Task<PackDrawTable?> GetAsync(int packId)
+    {
+        var config = await _db.PackDrawConfigs.FirstOrDefaultAsync(c => c.Id == packId);
+        if (config is null) return null;
+
+        var slotRates = await _db.PackDrawSlotRates
+            .Where(s => s.PackId == packId)
+            .ToListAsync();
+
+        var cardWeights = await _db.PackDrawCardWeights
+            .Where(w => w.PackId == packId)
+            .ToListAsync();
+
+        return new PackDrawTable
+        {
+            Config = config,
+            SlotRates = slotRates,
+            CardWeights = cardWeights,
+        };
+    }
+}