Phase 1: Extract Constants.cs and CommandRouter.cs

- Extract magic numbers (timer intervals, message type IDs, property keys) into Constants.cs
- Replace ~600-line HandleMmCommand switch with dictionary-based CommandRouter
- All /mm commands preserved with same behavior, now registered via lambdas
- PluginCore.cs and CharacterStats.cs updated to use named constants

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

MosswartMassacre/MosswartMassacre.csproj

@@ -304,6 +304,8 @@
     <Compile Include="..\Shared\VCS_Connector.cs">
       <Link>Shared\VCS_Connector.cs</Link>
     </Compile>
+    <Compile Include="CommandRouter.cs" />
+    <Compile Include="Constants.cs" />
     <Compile Include="ClientTelemetry.cs" />
     <Compile Include="DecalHarmonyClean.cs" />
     <Compile Include="FlagTrackerData.cs" />