Fix audit tool bootstrap and add per-run preflight

audit-code install-tools.sh:
- Buffer the opengrep release JSON before grep -m1; curl died with (23)
  under pipefail when grep quit early.
- Use ${m}: in the PowerShell block; $m: parsed as a scope-qualified var.
- On Arch, skip paru/yay when pacman -Q shows every package installed,
  since --needed still invokes sudo.
- Add --check-only (fast, installs nothing, non-zero naming missing tools)
  and --user-only (no system package managers, no sudo).

log-run.py (both skills): put the skill dir on sys.path so running it as
a script from any cwd no longer raises ModuleNotFoundError.

audit-terraform: move deps from requirements.txt into pyproject
dependency groups and add scripts/install-tools.sh (uv sync --group tools,
then check trivy, tflint, tofu, terragrunt, gh).

Both SKILL.md files gain a 0.5 Preflight step and call scripts through
uv run --project ${SKILL_DIR}. tools_unavailable is now a map of tool to
exact install command; audit-terraform skips trivy when absent and stops
with an install hint instead of crashing when tofu/terragrunt is missing.

plugins/reviews/skills/audit-terraform/scripts/refresh-controls.py

@@ -4,7 +4,7 @@ from __future__ import annotations
 import argparse
 import json
 import sys
-from datetime import datetime, timezone
+from datetime import datetime, timezone, UTC
 from pathlib import Path
 
 import requests
@@ -29,7 +29,7 @@ def _fetch(url: str) -> str:
 
 
 def _now() -> datetime:
-    return datetime.now(timezone.utc)
+    return datetime.now(UTC)
 
 
 def _build_fsbp() -> ControlsFile: