feat(config): MatchingConfig section with AI-fallback threshold

Adds a [ConfigSection("Matching")] POCO carrying the
RankBattleAiFallbackThresholdSeconds tunable (default 15). Auto-picked
up by EnsureSeedDataAsync's reflection-based ConfigSection seeder.
Consumed by InProcessPairUp in a later task.

GameConfigurationJsonbTests.EnsureSeedData_writes_one_row_per_ConfigSection_with_ShippedDefaults_payload
updated to include the new Matching section in its expected keys.

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

SVSim.Database/Models/Config/MatchingConfig.cs

@@ -0,0 +1,20 @@
+namespace SVSim.Database.Models.Config;
+
+/// <summary>
+/// Tunables for the in-process pair-up matching service. Today: just the AI-fallback
+/// threshold for rank-battle modes. The full matching-queue API is a separate spec;
+/// this config section lives alongside the placeholder.
+/// </summary>
+[ConfigSection("Matching")]
+public class MatchingConfig
+{
+    /// <summary>
+    /// How long (seconds) a viewer must have been parked in a PvpFirstThenAiFallback
+    /// queue before their next /do_matching poll resolves to an AI battle.
+    /// Defaults to 15 — matches the prod 4s pre-AIBattleStart pause plus a comfortable
+    /// polling cycle.
+    /// </summary>
+    public int RankBattleAiFallbackThresholdSeconds { get; set; } = 15;
+
+    public static MatchingConfig ShippedDefaults() => new();
+}

SVSim.UnitTests/Database/Config/MatchingConfigTests.cs

@@ -0,0 +1,34 @@
+using System.Linq;
+using NUnit.Framework;
+using SVSim.Database.Models.Config;
+
+namespace SVSim.UnitTests.Database.Config;
+
+[TestFixture]
+public class MatchingConfigTests
+{
+    [Test]
+    public void Default_threshold_is_15_seconds()
+    {
+        var cfg = new MatchingConfig();
+        Assert.That(cfg.RankBattleAiFallbackThresholdSeconds, Is.EqualTo(15));
+    }
+
+    [Test]
+    public void ShippedDefaults_returns_a_new_instance_with_default_threshold()
+    {
+        var cfg = MatchingConfig.ShippedDefaults();
+        Assert.That(cfg.RankBattleAiFallbackThresholdSeconds, Is.EqualTo(15));
+    }
+
+    [Test]
+    public void Has_ConfigSection_attribute_with_name_Matching()
+    {
+        var attr = typeof(MatchingConfig)
+            .GetCustomAttributes(typeof(ConfigSectionAttribute), false)
+            .Cast<ConfigSectionAttribute>()
+            .FirstOrDefault();
+        Assert.That(attr, Is.Not.Null);
+        Assert.That(attr!.Name, Is.EqualTo("Matching"));
+    }
+}

SVSim.UnitTests/Models/GameConfigurationJsonbTests.cs

@@ -25,13 +25,13 @@ public class GameConfigurationJsonbTests
         var rows = await db.GameConfigs.AsNoTracking().ToListAsync();
         var byName = rows.ToDictionary(r => r.SectionName);
 
-        // One row per [ConfigSection]-marked POCO (11 sections today: Player, DefaultGrants,
+        // One row per [ConfigSection]-marked POCO (12 sections today: Player, DefaultGrants,
         // DefaultLoadout, Challenge, Rotation, PackRates, MyRotationSchedule, Story, ResourceConfig,
-        // Freeplay, ArenaTwoPick).
+        // Freeplay, ArenaTwoPick, Matching).
         Assert.That(byName.Keys, Is.EquivalentTo(new[]
         {
             "Player", "DefaultGrants", "DefaultLoadout", "Challenge", "Rotation", "PackRates",
-            "MyRotationSchedule", "Story", "ResourceConfig", "Freeplay", "ArenaTwoPick",
+            "MyRotationSchedule", "Story", "ResourceConfig", "Freeplay", "ArenaTwoPick", "Matching",
         }));
 
         var resources = JsonSerializer.Deserialize<ResourceConfig>(byName["ResourceConfig"].ValueJson)!;