fix(ci): restore CI for pnpm/action-setup v6

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Summary

• update CI and publish workflows to use pnpm/action-setup v6
• fix auto-label output handling for JSON changed-files results and labels with spaces
• keep the workflow upgrade from PR build(deps): bump pnpm/action-setup from 4 to 6 #29 but avoid the broken workflow/output path

Refs agentgram-mcp PR #29.

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CI 실패: Lint, Build & Test (20). 수정 필요.

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CI 실패: Lint, Build & Test (20). 수정 필요.

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Review: REQUEST_CHANGES 🔄\n\nThis is the same regression pattern as agentgram/agentgram#429 before the fix. CI is still failing with ERR_PNPM_BROKEN_LOCKFILE, so the stated goal (restore CI for pnpm/action-setup@v6) is not achieved yet.\n\n### What failed\n- Lint, Build & Test (20) fails during pnpm install --frozen-lockfile\n- Exact error:\n\nERR_PNPM_BROKEN_LOCKFILE\nThe lockfile at .../pnpm-lock.yaml is broken: expected a single document in the stream, but found more\n\n\n### Assessment\n- auto-label fix looks good and worth keeping\n- But the workflow bump pnpm/action-setup@v4 -> v6 is still breaking CI in the same way we already saw elsewhere\n- So this PR still needs either:\n 1. explicit pnpm version pin + verified green CI, or\n 2. revert/stay on previous action version for now\n\n---\n🐱 Navi code review

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수동 리뷰 완료: 변경 범위가 워크플로 3개로 제한돼 있고, packageManager=pnpm@10.4.1과 CI 설정이 일치합니다. auto-label은 changed-files JSON 파싱과 multiline GITHUB_OUTPUT 처리를 바로잡아 label 이름 공백/빈 배열 케이스도 안전하게 처리합니다. blocking 이슈는 보이지 않았습니다. GitHub 정책상 작성자 본인 PR이라 approve는 불가했습니다.