fix: preserve existing hooks on install

[zerone0x]

Summary

• back up existing .claude/settings.json before writing hooks
• merge new hooks with existing entries instead of overwriting them
• add tests for preserving hooks and backup creation

Fixes #114.

Testing

• uv run pytest tests/test_skills.py -q

[tirth8205]

CI passed, but this now has merge conflicts with skills.py after PR #152 merged. Could you rebase on latest main? Once rebased, we'll merge immediately.

[tirth8205]

Thanks for tackling issue #114! The merge logic and backup approach are the right solution. However there are two bugs that need fixing before this can merge:

1. Missing encoding="utf-8" on write (regression)

The original install_hooks wrote with encoding="utf-8":

settings_path.write_text(json.dumps(existing, indent=2) + "\n", encoding="utf-8")

The PR drops the encoding parameter:

settings_path.write_text(json.dumps(existing, indent=2) + "\n")

On Windows with non-UTF-8 system locale this will break. Please restore encoding="utf-8".

2. Hook format generated is invalid

The PR still calls the original generate_hooks_config() which emits:

• A PreCommit hook — this is not a valid Claude Code hook event
• Flat {"matcher": ..., "command": ..., "timeout": ...} structure instead of the correct nested {"matcher": ..., "hooks": [{"type": "command", "command": ..., "timeout": ...}]} structure

These bugs were also present before this PR, but since you're changing the merge logic it would be good to fix the format here too. PR #192 has the correct format if you want to pull from it.

The backup creation and merge loop logic itself is correct — just these two things to fix.