Anade pkg/tools/devicemesh con Client HTTP al device_agent + ToolRegistry
con 16 tools standard (exec, fs.*, git.*, docker.*, proc.*, pkg.*, shell.eval).
RegisterBuiltins filtra por mode user/sudo via RequiresApproval flag.
Hook al pkg/decision con ActionKindDeviceMesh + DeviceMeshAction.
Runner soporta dispatch via NewRunnerWithDeviceMesh (back-compat NewRunner).
Tests: 25 nuevos en devicemesh + 4 en runner. Build clean.
