feat(config): add CardMasterConfig section (CurrentHash + EnableServing)

SVSim.Database/Models/Config/CardMasterConfig.cs

@@ -0,0 +1,35 @@
+namespace SVSim.Database.Models.Config;
+
+/// <summary>
+/// Tunables for serving the card-master payload at <c>POST /immutable_data/card_master</c>.
+/// V1 ships the captured prod blob verbatim; the hash here pins to that capture's prod hash
+/// so any client whose <c>cardmaster/card_master_1</c> was seeded from a prod dump skips
+/// re-download.
+/// </summary>
+[ConfigSection("CardMasterConfig")]
+public class CardMasterConfig
+{
+    /// <summary>
+    /// Emitted on <c>/load/index</c> response's inner <c>data.card_master_hash</c> when the
+    /// request's <c>card_master_hash</c> body field doesn't match this value. Client treats
+    /// the string as opaque (presence-only check, value is echoed back unchanged on the next
+    /// <c>/immutable_data/card_master</c> request). Format <c>&lt;sha1 hex&gt;:&lt;CardMasterId&gt;</c>.
+    /// <para>
+    /// Default value is the prod-captured hash paired with the blob at
+    /// <c>SVSim.EmulatedEntrypoint/Data/card_master_2026-06-03.txt</c>. When swapping the
+    /// blob, update this string in lockstep — the hash is otherwise free-form (the client
+    /// never validates its structure).
+    /// </para>
+    /// </summary>
+    public string CurrentHash { get; set; } = "94b5c44edc51ff76c0af8fcc894af12f979dd38c:1";
+
+    /// <summary>
+    /// Kill switch. When false, <c>/immutable_data/card_master</c> returns 503 and
+    /// <c>/load/index</c> never emits <c>card_master_hash</c>. Useful for shaving the 1.27 MB
+    /// download out of test-only deployments where the test viewers already have a seeded
+    /// local cache.
+    /// </summary>
+    public bool EnableServing { get; set; } = true;
+
+    public static CardMasterConfig ShippedDefaults() => new();
+}