Fix: Harden commit-msg hook (trap cleanup, pattern, blank line)

[rubambiza]

Summary

Hardens scripts/hooks/commit-msg, mirroring fixes reviewed on the ported copy in kagenti/agent-skills#14:

• Temp-file cleanup via trap — trap 'rm -f "$TEMP_FILE"' EXIT so the temp file is removed on any exit path (including early exit under set -euo pipefail).
• Simplify strip pattern — drop the redundant cursor alternate; grep -i already matches Cursor case-insensitively in (Claude|Cursor|anthropic).
• Guard double blank line — only prepend a blank before the Assisted-By trailer when the message does not already end with one.

Verified: a message containing Co-authored-by: Claude converts to a single-blank-separated Assisted-By trailer; a message with no AI trailer is left untouched.

Fixes #17

Assisted-By: Claude Code

[clawgenti]

This PR cleanly hardens the commit-msg hook with three well-scoped fixes. All checks pass. Ready for human review.

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Reviewed by clawgenti using github:pr-review

[mrsabath]

Summary

Clean, correct hardening of the commit-msg hook. I verified all three fixes by running the reconstructed hook against representative messages:

1. trap cleanup — trap 'rm -f "$TEMP_FILE"' EXIT replaces the trailing rm, so the temp file is removed on every exit path under set -euo pipefail (including an early exit between mktemp and the old rm). $TEMP_FILE is set before the trap and properly quoted. ✓
2. simplified strip pattern — dropping the redundant |cursor is safe: grep -i already matches lowercase cursor via Cursor. Confirmed directly — no behavior change. ✓
3. double-blank guard — exactly one blank line precedes the Assisted-By trailer. Verified the three cases: Co-authored-by: Claude → single-blank-separated Assisted-By; no-AI-trailer message left untouched; body already ending in a blank line does not produce a double blank. ✓

Properly quoted, idiomatic, and consistent with the file's style; the inline comment explaining the guard is helpful. All checks pass (DCO, PR title, add-to-project). The clawgenti bot already completed its automated pass — this adds the human-review approval.

Areas reviewed: Shell, Security, Commit conventions
Author: rubambiza (MEMBER)
Commits: 2, signed-off (DCO ✓)
CI: passing