NEO-146: fix remaining C# analyzer style warnings

Apply using simplification, inline declarations, const locals, and
Lock in PostgresDockerHelper; document RCS1118 and IDE0018 in style guide.

.cursor/rules/csharp-style.md

@@ -81,6 +81,18 @@ return query.ToArray();
 - **Keep braced `using (var …) { … }`** when the block has **multiple statements** (Arrange + Act + Assert inside one scope, seed loops, or any sequence that shares locals).
 - **Do not flatten** multi-statement blocks into `using var` at method scope when inner scopes reuse names like `store`, `registry`, or `scope` — that causes **CS0136** name clashes. Use distinct names (`seedStore`, `actScope`, `readStore`) or keep the braced block.
 
+## Local `const` (RCS1118)
+
+- When a local is initialized from a **compile-time constant** (string literal, numeric literal, or `public const` field), declare it **`const`** instead of **`var`**.
+
+```csharp
+const string questId = PrototypeE7M1QuestCatalogRules.GatherIntroQuestId;
+```
+
+## Inline declarations (IDE0018)
+
+- Prefer **inline initialization** over declare-then-assign when the analyzer suggests it, e.g. `var outcome = Operation(...)` and `TryGet(..., out var snapshot)` instead of separate upfront declarations.
+
 ```csharp
 // Prefer — single disposable, single follow-on statement
 await using var conn = new NpgsqlConnection(cs);

server/NeonSprawl.Server.Tests/Game/Contracts/ContractOutcomePersistenceIntegrationTests.cs

@@ -85,8 +85,7 @@ public sealed class ContractOutcomePersistenceIntegrationTests(PostgresIntegrati
             [],
             RecordedAt);
 
-        using (var scope = Factory.Services.CreateScope())
-        {
+        using var scope = Factory.Services.CreateScope();
         var instanceStore = scope.ServiceProvider.GetRequiredService<IContractInstanceStore>();
         var outcomeStore = scope.ServiceProvider.GetRequiredService<IContractOutcomeStore>();
         Assert.True(instanceStore.TryCreateActive(
@@ -104,7 +103,6 @@ public sealed class ContractOutcomePersistenceIntegrationTests(PostgresIntegrati
         Assert.False(duplicateId);
         Assert.False(duplicateKey);
     }
-    }
 
     [RequirePostgresFact]
     public async Task TryAppend_ShouldReturnFalse_WhenContractInstanceMissing()

server/NeonSprawl.Server.Tests/Game/Gathering/ResourceNodeInstancePersistenceIntegrationTests.cs

@@ -57,14 +57,12 @@ public sealed class ResourceNodeInstancePersistenceIntegrationTests(PostgresInte
         }
 
         // Act
-        ResourceNodeInstanceMutationOutcome denyOutcome;
-        ResourceNodeInstanceSnapshot persisted;
         await using var secondFactory = new PostgresWebApplicationFactory();
         using var actScope = secondFactory.Services.CreateScope();
         var actRegistry = actScope.ServiceProvider.GetRequiredService<IResourceNodeDefinitionRegistry>();
         var actStore = actScope.ServiceProvider.GetRequiredService<IResourceNodeInstanceStore>();
-        denyOutcome = ResourceNodeInstanceOperations.TryCommitSuccessfulGatherDecrement(AlphaId, actRegistry, actStore);
-        actStore.TryGetRemainingGathers(AlphaId, out persisted);
+        var denyOutcome = ResourceNodeInstanceOperations.TryCommitSuccessfulGatherDecrement(AlphaId, actRegistry, actStore);
+        actStore.TryGetRemainingGathers(AlphaId, out var persisted);
 
         // Assert
         Assert.Equal(ResourceNodeInstanceMutationKind.Denied, denyOutcome.Kind);

server/NeonSprawl.Server.Tests/Game/PositionState/PostgresDockerHelper.cs

@@ -1,4 +1,5 @@
 using System.Diagnostics;
+using System.Threading;
 using Npgsql;
 
 namespace NeonSprawl.Server.Tests.Game.PositionState;
@@ -13,7 +14,7 @@ namespace NeonSprawl.Server.Tests.Game.PositionState;
 /// </remarks>
 internal static class PostgresDockerHelper
 {
-    private static readonly object StateLock = new();
+    private static readonly Lock StateLock = new();
     private static Task? _ensureTask;
     private static bool _composeStartedByUs;
     private static string? _repoRoot;

server/NeonSprawl.Server.Tests/Game/Quests/PlayerQuestProgressPersistenceIntegrationTests.cs

@@ -22,7 +22,7 @@ public sealed class PlayerQuestProgressPersistenceIntegrationTests(PostgresInteg
         // Arrange
         await ResetQuestProgressTableAsync();
         const int concurrentCalls = 8;
-        var questId = PrototypeE7M1QuestCatalogRules.GatherIntroQuestId;
+        const string questId = PrototypeE7M1QuestCatalogRules.GatherIntroQuestId;
 
         // Act
         var results = await Task.WhenAll(
@@ -93,7 +93,7 @@ public sealed class PlayerQuestProgressPersistenceIntegrationTests(PostgresInteg
     {
         // Arrange
         await ResetQuestProgressTableAsync();
-        var questId = PrototypeE7M1QuestCatalogRules.GatherIntroQuestId;
+        const string questId = PrototypeE7M1QuestCatalogRules.GatherIntroQuestId;
 
         // Act
         using (var firstScope = Factory.Services.CreateScope())

server/NeonSprawl.Server/Game/Quests/PrototypeE7M3QuestFactionRules.cs

@@ -107,7 +107,7 @@ public static class PrototypeE7M3QuestFactionRules
     /// <summary>Returns a human-readable error if grid contract quest shape fails, otherwise <see langword="null"/>.</summary>
     public static string? TryGetGridContractShapeError(IReadOnlyDictionary<string, QuestDefRow> rowsById)
     {
-        var qid = PrototypeE7M1QuestCatalogRules.GridContractQuestId;
+        const string qid = PrototypeE7M1QuestCatalogRules.GridContractQuestId;
         if (!rowsById.TryGetValue(qid, out var row))
             return $"error: missing quest '{qid}'";