docs(desktop): Name ptrace_scope 2 as where proot-next runs restricted
6df494e said proot-next runs in a restricted mode wherever Yama
refuses ptrace, scope 2 or 3, and that the CAP_SYS_PTRACE copy runs it
in its ptrace mode there. Only scope 2 was measured, and at scope 3 no
capability attaches at all, so the texts now name scope 2.
Measured with desktop:main-ubuntu26.04 (proot-apps 0.5.10, proot-next
0.3.9) under Docker, by proot-next's own -v 1 notes: at scope 1 the
plain copy runs in ptrace mode, and with --cap-add SYS_PTRACE the
wrapper links the capability copy, also ptrace mode; at scope 2 without
the capability the plain copy runs in the guest-stub mode, and with it
the wrapper links the capability copy, which runs in ptrace mode. In all
four, check passes and Geany installs, runs and is removed.