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>

ProjectSettings/NetCodeClientAndServerSettings.asset

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+  CurrentImportanceSuggestions:
+  - MinValue: 1
+    MaxValue: 4
+    Name: Low Importance
+    Tooltip: For cosmetic (i.e. visual-only) ghosts like glass bottles, signs, beach-balls,
+      and cones etc. Typically <b>Static</b>.
+  - MinValue: 5
+    MaxValue: 40
+    Name: Medium Importance
+    Tooltip: For common gameplay-affecting ghosts like trees, doors, explosive barrels,
+      dropped loot etc. Typically <b>Static</b>.
+  - MinValue: 50
+    MaxValue: 250
+    Name: High Importance
+    Tooltip: For per-player and objective-critical ghosts like Player Character Controllers
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+  - MinValue: 1000
+    MaxValue: 0
+    Name: Critical Importance
+    Tooltip: For gameplay critical singletons like the one keeping the current score,
+      or the one denoting whether or not the current round has started etc. Choose
+      <b>UsePreSerialization</b>, and use sparingly.