fix(skills): add PATH guard and remove absolute paths from hooks

[itxaiohanglover]

Summary

Fixes two related bugs in generate_hooks_config():

• Generated Claude Code hooks fail noisily when the binary is not on PATH, and fire on every Bash command #549: Hooks called bare code-review-graph without checking PATH. When installed in a project venv, every Edit/Write/Bash tool call surfaced code-review-graph: not found. Also, the Bash matcher fired on every shell command (git status, ls, test runs), not just file mutations.
• [Bug]: claude-code hooks in settings.json shall not contain absolute paths to the repo #558: Hooks embedded json.dumps(repo_root.resolve().as_posix()) — an absolute path — making .claude/settings.json non-shareable across collaborators with different checkout paths.

Changes

PATH guard (#549)

# Before
"command": "cat >/dev/null || true; git rev-parse --git-dir >/dev/null 2>&1 && code-review-graph update ..."

# After
"command": "cat >/dev/null || true; command -v code-review-graph >/dev/null 2>&1 || exit 0; git rev-parse --git-dir >/dev/null 2>&1 && code-review-graph update ..."

This mirrors the pattern already used by the git pre-commit hook installed by the same install command.

Narrowed matcher (#549)

# Before
"matcher": "Edit|Write|Bash"

# After
"matcher": "Edit|Write"

Edit|Write covers the cases where the graph can actually become stale from within Claude Code. Bash-driven file mutations are rare and the cost of firing on every shell command is high.

Dynamic repo root (#558)

# Before
--repo "/home/username/work/some/path/to/depot"

# After
--repo "$(git rev-parse --show-toplevel 2>/dev/null)"

The repo_root parameter is retained for backward compatibility but no longer embedded in commands.

Test plan

• test_hooks_have_path_guard — verifies both hooks include command -v code-review-graph
• test_hooks_use_dynamic_repo_root — verifies both hooks use git rev-parse --show-toplevel
• test_hooks_no_absolute_path_embedded — verifies no hardcoded path appears in commands
• test_post_tool_use_matcher_excludes_bash — verifies matcher is Edit|Write, not Edit|Write|Bash
• All 144 existing skills tests still pass
• ruff check passes (no new lint errors introduced)

Closes #549, #558