Move the code and terraform audits into the reviews plugin

Copy the standalone code-review and terraform-review skills into
plugins/reviews as audit-code and audit-terraform. The rename separates the
automated, linter-driven audits from the guided review-pr walkthrough that
already lived here.

Resolve bundled script paths through ${SKILL_DIR}, exported in a new step 0.
CLAUDE_PLUGIN_ROOT is not set in the Bash tool environment, so the obvious
substitution would have expanded to nothing and broken every collection
script invocation.

Replace the PLAN and DESIGN docs with READMEs written from the current
SKILL.md and scripts. The old docs had drifted badly: they named semgrep
where the code calls opengrep, scoped five review agents where there are
now eight, and predated Lua, PowerShell, and GitHub Actions support.

Add CONSISTENCY_NORMS to the audit-terraform agent inputs. The collection
script writes consistency_norms.json and the agent prompt declares it, but
SKILL.md never listed it, leaving the variable unsubstituted.

Drop the --ingest-verdicts instruction from both skills. review_stats.py
parses no arguments, so the ref-mode verdict template it told users to feed
back could never be read.

Point audit-terraform's smoke test at README.md and resolve its fixture
paths relative to the test file rather than an absolute home directory.

Tests: 197 passing (audit-code), 106 passing (audit-terraform).

plugins/reviews/skills/audit-terraform/agents/cis-reviewer.md

@@ -0,0 +1,35 @@
+# cis-reviewer agent
+
+Legacy fallback reviewer for the CIS AWS Foundations Benchmark.
+
+This prompt is not part of the default review path anymore. The default flow
+uses Trivy for first-pass benchmark-style detection, then `aws-bp-reviewer`
+for contextual triage and AWS-specific judgment.
+
+## When to use
+
+Use only when explicitly asked to cross-check Trivy findings against CIS or
+when the default Trivy-first path needs benchmark-specific confirmation.
+
+## Inputs
+
+- `MANIFEST` — agent slice produced by `collect-changes.py`
+- `REPO` — repo root / worktree path
+- `OUTPUT` — path to write findings JSON
+
+## Default behavior
+
+1. Read `trivy_findings` from `MANIFEST` first.
+2. Treat Trivy as the source of first-pass CIS-style detection.
+3. Only emit a CIS finding when:
+   - Trivy surfaced an issue that needs CIS labeling or confirmation, or
+   - you find a high-confidence CIS gap that Trivy clearly missed.
+4. Avoid live docs lookups in the default fallback path unless the user
+   explicitly asked for benchmark confirmation and the needed mapping is absent.
+
+## Rules
+
+- Minimize overlap with Trivy and `aws-bp-reviewer`.
+- Avoid re-reporting low-signal benchmark findings already present in
+  `trivy_findings`.
+- Write only the JSON findings document to `OUTPUT`.