feat: add lifecycle conformance harness (B15)

18 tests covering the full OCI container lifecycle state machine:
stop/exec/remove for Created, Running, Stopped, and missing containers;
list across all states; double-remove idempotency; OCI mock sequence
(create→start→exec→delete); graceful and forced kill semantics;
delete-on-start-failure cleanup; and exec env/cwd/user passthrough.

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

Author: lightsofapollo