feat(inventory): add GrantSource enum + message lookup

Introduces GrantSource (17 values, DB-persisted) and GrantSourceMessages.For()
for the item-acquire-history feature. Values 1/2 mirror prod captures;
coverage test verifies every enum value has a non-empty message.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

SVSim.Database/Services/Inventory/GrantSource.cs

@@ -0,0 +1,61 @@
+namespace SVSim.Database.Services.Inventory;
+
+/// <summary>
+/// Logical source of a grant routed through <see cref="IInventoryTransaction.GrantAsync"/>.
+/// Stored verbatim in <c>viewer_acquire_history.AcquireType</c> and surfaced on the
+/// <c>/item_acquire_history/info</c> wire as <c>acquire_type</c>.
+/// </summary>
+/// <remarks>
+/// Values are persisted to the database — renumbering after ship requires a migration.
+/// Values 1 and 2 mirror the prod capture in
+/// <c>data_dumps/captures/traffic_prod_misc_clicking.ndjson</c>; the rest are our own.
+/// </remarks>
+public enum GrantSource
+{
+    Unknown = 0,
+    DailyBonus = 1,
+    PackOpen = 2,
+    PuzzleReward = 3,
+    StoryFinish = 4,
+    BattlePassClaim = 5,
+    MissionReward = 6,
+    ArenaTwoPickFinish = 7,
+    ItemPurchase = 8,
+    BuildDeckBuy = 9,
+    SleeveBuy = 10,
+    LeaderSkinBuy = 11,
+    GachaPointExchange = 12,
+    AchievementReward = 13,
+    SerialCodeRedeem = 14,
+    CardCosmeticCascade = 15,
+    AdminGrant = 99,
+}
+
+/// <summary>
+/// Pre-localized text written into the <c>message</c> field of an item-acquire-history row.
+/// The client renders this string verbatim, so all entries are user-facing English.
+/// </summary>
+public static class GrantSourceMessages
+{
+    public static string For(GrantSource source) => source switch
+    {
+        GrantSource.Unknown             => "Unknown",
+        GrantSource.DailyBonus          => "Daily Bonus",
+        GrantSource.PackOpen            => "From buying card packs",
+        GrantSource.PuzzleReward        => "From puzzle reward",
+        GrantSource.StoryFinish         => "From story reward",
+        GrantSource.BattlePassClaim     => "From battle pass reward",
+        GrantSource.MissionReward       => "From mission reward",
+        GrantSource.ArenaTwoPickFinish  => "From 2Pick reward",
+        GrantSource.ItemPurchase        => "From shop purchase",
+        GrantSource.BuildDeckBuy        => "From starter set purchase",
+        GrantSource.SleeveBuy           => "From sleeve purchase",
+        GrantSource.LeaderSkinBuy       => "From leader skin purchase",
+        GrantSource.GachaPointExchange  => "From point exchange",
+        GrantSource.AchievementReward   => "From achievement reward",
+        GrantSource.SerialCodeRedeem    => "From serial code",
+        GrantSource.CardCosmeticCascade => "Card cosmetic",
+        GrantSource.AdminGrant          => "From admin grant",
+        _ => throw new ArgumentOutOfRangeException(nameof(source), source, "Unhandled GrantSource"),
+    };
+}