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/add-parallel/SKILL.md

@@ -48,9 +48,9 @@ PARALLEL_API_KEY=...
 ## 5. 빌드와 검증
 
 ```bash
-npm run build:runners
-npm run build
-npm run setup -- --step service
+bun run build:runners
+bun run build
+bun run setup -- --step service
 ```
 
 디스코드 테스트 예시: