chore: replace all node/npm/tsx references with bun across codebase

- Source: setup/service.ts, runners.ts, agent-runner.ts error messages
- Scripts: restart-stack.sh, run-migrations.ts → bun
- Bootstrap: setup.sh check_node→check_bun, npm install→bun install
- Docs: CLAUDE.md, README.md, all SKILL.md files
- Tests: service.test.ts, restart-stack.test.ts expectations updated

.claude/skills/customize/SKILL.md

@@ -58,13 +58,13 @@ description: Customize Discord-only EJClaw behavior, routing, integrations, prom
 작게 바꿨으면 최소 이 정도는 확인합니다.
 
 ```bash
-npm run typecheck
-npm test
+bun run typecheck
+bun test
 ```
 
 러너나 실행 경로를 건드렸으면 추가로 확인합니다.
 
 ```bash
-npm run build:runners
-npm run setup -- --step verify
+bun run build:runners
+bun run setup -- --step verify
 ```