feat(inventory): scaffold InventoryService namespace types

Empty interfaces + records for IInventoryService, IInventoryTransaction,
InventoryCommitResult, InventoryLoadConfig, InventoryCatalogException.
Implementation lands in subsequent commits.

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

SVSim.Database/Services/Inventory/InventoryCommitResult.cs

@@ -0,0 +1,20 @@
+using SVSim.Database.Services;
+
+namespace SVSim.Database.Services.Inventory;
+
+/// <summary>
+/// Result of <see cref="IInventoryTransaction.CommitAsync"/>.
+/// <para>
+/// <see cref="RewardList"/> — wire-shape entries with currency-collision resolved (one entry per
+/// (type, id); for currencies that were both spent and granted, the last post-state in op order
+/// wins). Use this for response <c>reward_list</c> fields.
+/// </para>
+/// <para>
+/// <see cref="Deltas"/> — verbatim ordered (type, id, num) sequence the caller queued. No
+/// collapse, no cosmetic-cascade entries. Use this for BP <c>achieved_info</c> and Story
+/// <c>story_reward_list</c> popups.
+/// </para>
+/// </summary>
+public sealed record InventoryCommitResult(
+    IReadOnlyList<GrantedReward> RewardList,
+    IReadOnlyList<GrantedReward> Deltas);