🛡️ Sentinel: [HIGH] Fix unit teleportation and unauthorized movement

[google-labs-jules]

🚨 Severity: HIGH
💡 Vulnerability: Unit teleportation and unauthorized movement.
🎯 Impact: Players could teleport units anywhere on the map or move units belonging to other players by sending manipulated commands to the server.
🔧 Fix: Added server-side ownership and adjacency checks in UnitCommandHandler.moveUnit.
✅ Verification: Added unit tests in src/server/game/Security.test.ts covering teleportation and unauthorized movement scenarios.

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PR created automatically by Jules for task 1241878146137501230 started by @b0x1

[google-labs-jules]

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