[codex] start fork skill daemon

[longfin]

What changed

• The fork-into-container skill now starts the matching vicoop-client --runtime container daemon in the background by default after harness injection.
• Added pid/log tracking under a per-kind state directory, with reuse for an already-live skill-owned daemon.
• Added VICOOP_FORK_DAEMON=manual|start|restart|stop and VICOOP_FORK_STATE_DIR controls.
• Updated skill docs to describe daemon ownership, logs, and the limits around session-end cleanup.

Why

Forking into a container is easier to use when the bridge daemon is already running after the skill finishes. The implementation keeps the ownership boundary narrow: it only stops or reuses a pidfile-backed process whose command line matches the expected backend/runtime flags.

Validation

• bash -n skills/fork-into-container/fork.sh
• shellcheck skills/fork-into-container/fork.sh
• VICOOP_FORK_KIND=codex VICOOP_FORK_DAEMON=stop VICOOP_FORK_STATE_DIR=$(mktemp -d -t vicoop-fork-test.XXXXXX) bash skills/fork-into-container/fork.sh
• git diff --check -- skills/fork-into-container/fork.sh skills/fork-into-container/SKILL.md