v2.3.9: Fix stalled processes and AOT cache crash

- Auto-kill stalled HytaleClient/java processes before launch and repair
  (cross-platform: Windows taskkill+PowerShell, macOS/Linux pkill)
- Remove HytaleServer.aot before launch to prevent incompatible AOT cache
  causing fastutil ClassNotFoundException on singleplayer
- safeRemoveDirectory auto-kills processes on EPERM/EBUSY before retry

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

backend/managers/gameLauncher.js

@@ -27,6 +27,7 @@ const { ensureGameInstalled } = require('./differentialUpdateManager');
 const { syncModsForCurrentProfile } = require('./modManager');
 const { getUserDataPath } = require('../utils/userDataMigration');
 const { syncServerList } = require('../utils/serverListSync');
+const { killGameProcesses } = require('./gameManager');
 
 // Client patcher for custom auth server (sanasol.ws)
 let clientPatcher = null;
@@ -436,6 +437,22 @@ exec "$REAL_JAVA" "\${ARGS[@]}"
     }
   }
 
+  // Kill any stalled game processes from a previous launch to prevent file locks
+  // and "game already running" issues
+  await killGameProcesses();
+
+  // Remove AOT cache: generated by official Hytale JRE, incompatible with F2P JRE.
+  // Client adds -XX:AOTCache when this file exists, causing classloading failures.
+  const aotCache = path.join(gameLatest, 'Server', 'HytaleServer.aot');
+  if (fs.existsSync(aotCache)) {
+    try {
+      fs.unlinkSync(aotCache);
+      console.log('Removed incompatible AOT cache (HytaleServer.aot)');
+    } catch (aotErr) {
+      console.warn('Could not remove AOT cache:', aotErr.message);
+    }
+  }
+
   // DualAuth Agent: Set JAVA_TOOL_OPTIONS so java picks up -javaagent: flag
   // This enables runtime auth patching without modifying the server JAR
   const agentJar = path.join(gameLatest, 'Server', 'dualauth-agent.jar');