fix hook context output

[danielmorozoff]

Summary

• Fix PreToolUse hook output to emit top-level systemMessage instead of unsupported hookSpecificOutput.additionalContext.
• Add a regression test covering unsupported hook fields.
• Ignore local assistant artifacts in .gitignore.

Why

Newer CLI versions reject hook output containing additionalContext with:

PreToolUse hook returned unsupported additionalContext

The generated hook had regressed to a Claude-specific output shape.

Validation

• .venv/bin/pip install -e '.[all]'
• .venv/bin/pip check
• env HOME=/tmp/graphify-pytest-home .venv/bin/python -m pytest -q
• .venv/bin/graphify update .
• Smoke-tested the platform install and verified the generated hook output contains systemMessage and no additionalContext.