Set up DOTS + Netcode for Entities foundation

One-time stack setup per Docs/dots-setup-task.md (Unity 6.4.7 / 6000.4.7f1).
Packages: entities 6.4.0, entities.graphics 6.4.0, netcode 1.13.2, physics 1.4.6.

- Assets/_Project asmdef split: ProjectM.Simulation/Client/Server/Authoring (root ns ProjectM)
- GameBootstrap : ClientServerBootstrap; verified separate client + server worlds in Play Mode
- Gameplay subscene wired into SampleScene as a baking target
- Heartbeat component + Burst ISystem; EditMode smoke test green (1/1)
- In-repo Obsidian vault (Docs/Vault) incl. DR-001 (plain-Entities test over internal NetCodeTestWorld)
- Portable .mcp.json (basic-memory + serena via ${CLAUDE_PROJECT_DIR}); CLAUDE.md conventions
- .gitignore for DOTS baking cache + machine-local config

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Assets/_Project/Tests/EditMode/ProjectM.Tests.EditMode.asmdef

@@ -0,0 +1,27 @@
+{
+    "name": "ProjectM.Tests.EditMode",
+    "rootNamespace": "ProjectM.Tests",
+    "references": [
+        "ProjectM.Simulation",
+        "Unity.Entities",
+        "Unity.Collections",
+        "Unity.Mathematics",
+        "UnityEngine.TestRunner",
+        "UnityEditor.TestRunner"
+    ],
+    "includePlatforms": [
+        "Editor"
+    ],
+    "excludePlatforms": [],
+    "allowUnsafeCode": false,
+    "overrideReferences": true,
+    "precompiledReferences": [
+        "nunit.framework.dll"
+    ],
+    "autoReferenced": false,
+    "defineConstraints": [
+        "UNITY_INCLUDE_TESTS"
+    ],
+    "versionDefines": [],
+    "noEngineReferences": false
+}