feat: atomic profile writes via shared lib (DOJ-2428)

[dbejarano820]

Summary

• Created scripts/lib/profile-io.sh with atomic write (temp+mv) pattern
• Updated all 4 hook scripts to use shared library
• Merged dual jq passes into single-pass operations
• Preserved jq-missing fallback and exit 0 convention

Test plan

• bash -n passes on all scripts
• No direct profile.json writes outside the lib
• Scripts still output correct JSON to stdout
• Profile writes use temp+mv pattern

Closes DOJ-2428

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[dbejarano820]

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