refactor(skills): rename tmux-agent-orchestrate-delete -> stop (step 1)

User decision: 2-step approach (Step 1 = simple rename, Step 2 = option
redefinition in a separate round).

Changes (mechanical, history preserved):
- skills/tmux-agent-orchestrate-delete/ -> skills/tmux-agent-orchestrate-stop/ (git mv)
- scripts/delete_session.sh -> scripts/stop_session.sh (git mv)
- sed s/orchestrate-delete/orchestrate-stop/g + delete_session.sh->stop_session.sh
  across 7 files (0 residual of either pattern)
- SKILL.md frontmatter 'name' -> tmux-agent-orchestrate-stop
- related_skills / companion refs in create/status/monitor/resume SKILL.md updated

NOT in this commit (deferred to step 2):
- Option redefinition (--purge-conversation, --mode soft clarification)
- Deprecation shim (external consumers = 0, no need)

6-route surface preserved (create/resume/stop/status/monitor + delegate-job).

Verified on isolated server -L claude-rename-step1-test (kill-server after):
- syntax PASS (all .sh + py_compile)
- E2E via renamed stop_session.sh: capture-id records id + status=stopped,
  status.sh renders it (DRIFT=-), idempotency exit 0
- 0 stale 'tmux-agent-orchestrate-delete' / 'delete_session' references
- git history preserved (rename detected as R)
- Global skill untouched; real YAML + main canary -L multi-agent-canary untouched

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

skills/tmux-agent-orchestrate-create/scripts/create_session.sh

@@ -90,7 +90,7 @@ fi
 
 # 이미 살아있으면 실패
 if _tmux has-session -t "$SESSION_NAME" 2>/dev/null; then
-  echo "ERROR: tmux session '$SESSION_NAME' already exists. Use tmux-agent-orchestrate-resume to attach, or tmux-agent-orchestrate-delete first." >&2
+  echo "ERROR: tmux session '$SESSION_NAME' already exists. Use tmux-agent-orchestrate-resume to attach, or tmux-agent-orchestrate-stop first." >&2
   exit 3
 fi
 
@@ -274,5 +274,5 @@ if [ -n "${TMUX_SERVER_NAME:-}" ] && [ "$TMUX_SERVER_NAME" != "default" ]; then
 else
   echo "Attach:  tmux attach -t $SESSION_NAME"
 fi
-echo "Delete:  use tmux-agent-orchestrate-delete skill"
+echo "Delete:  use tmux-agent-orchestrate-stop skill"
 echo "Resume:  use tmux-agent-orchestrate-resume skill (after first message creates a session id)"