test: use threads for core vitest projects

vitest.agents.config.ts

@@ -5,7 +5,6 @@ export function createAgentsVitestConfig(env?: Record<string, string | undefined
     dir: "src/agents",
     env,
     name: "agents",
-    pool: "forks",
   });
 }
 

vitest.commands.config.ts

@@ -5,7 +5,6 @@ export function createCommandsVitestConfig(env?: Record<string, string | undefin
     dir: "src/commands",
     env,
     name: "commands",
-    pool: "forks",
   });
 }
 

vitest.gateway.config.ts

@@ -5,7 +5,6 @@ export function createGatewayVitestConfig(env?: Record<string, string | undefine
     dir: "src/gateway",
     env,
     name: "gateway",
-    pool: "forks",
   });
 }