Prevents data loss from concurrent/interrupted state file writes by using
atomic write pattern (write to .tmp, then rename).
Changes:
- Add internal/util package with AtomicWriteJSON/AtomicWriteFile helpers
- Update witness/manager.go saveState to use atomic writes
- Update refinery/manager.go saveState to use atomic writes
- Update crew/manager.go saveState to use atomic writes
- Update daemon/types.go SaveState to use atomic writes
- Update polecat/namepool.go Save to use atomic writes
- Add comprehensive tests for atomic write utilities
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>