e2e: assert_stopped should take a target so the --quic stop leg reuses it

open   by a73x

test/e2e_05_session.sh's --quic stop leg grades the stop by the pid going away with its own loop; test/e2e_lib.sh assert_stopped does the same for --sock. Extend assert_stopped to take the target spelling (--sock PATH | --quic HOST:PORT) so the two doors are graded by one function. Also: the CLAUDE.md trail list omits the 'adopted across upgrade' line and the start-refusal's different shape; serve.Unlink.spared_successor is also what a non-socket inode at the path reports.