feat(llm-security)!: v8 Phase 3 complete - riskScoreV1, posture heuristic, docs

Closes Phase 3 (B11) of the v8.0.0 plan. Three parts, all with the failing
test written first.

riskScoreV1 removed. scanners/lib/severity.mjs drops riskScoreV1() and its
SEVERITY_WEIGHTS_V1 table - @deprecated since v7.0.0, kept for diff/comparison,
zero callers in code or tests (re-verified, not taken from the plan). The v1
weights are recorded in CHANGELOG so an old score stays re-derivable. riskScore
(v2) is untouched; a test pins that one critical still lands in the 70-95 tier
and that 50 lows score below it, which is exactly the case v1 collapsed to 100.

Posture category 12 no longer keys off an identifier name. The check was
/TRIFECTA_MODE/i over the session-guard source, which measured what a constant
was CALLED rather than whether enforcement was configurable. With the env-var
gone, that regex would have dropped every correctly-migrated project from PASS
to PARTIAL - the gate punishing the migration it exists to encourage. It now
matches getPolicyValue('trifecta', 'mode', ...) and still accepts a pre-v8
vendored guard reading the old env-var, because a third-party project carries
its own hook copy and is equally configurable either way; the evidence line
says which of the two was found. The PARTIAL finding recommended setting an
env-var that v8 ignores; it now names the policy key. The grade-a fixture hook
moves to the policy-era form.

Two never-implemented env-vars deleted from the docs. LLM_SECURITY_SCR_OFFLINE
(ci-cd-guide) and LLM_SECURITY_OFFLINE (supply-chain-attack example) were
documented as OSV.dev / npm-audit kill-switches. No code has ever read either -
verified by grep across scanners, hooks and scripts, which finds them only in
markdown. A promised kill-switch that does nothing is worse than a documented
absence: it is trusted precisely when the run is meant to be air-gapped. The
docs now say there is none and that egress must be blocked at the network
layer. The LLM_SECURITY_AUDIT_* wildcard is narrowed to the one real key.

Docs. Migration section in README + CHANGELOG with the env-var -> policy-key
table, the detection commands (env + shell rc + .envrc + workflows), and the
explicit warning that a removed variable is now INERT rather than an error -
which is the failure mode that loses a project its configuration silently. The
hardening-guide env table splits into surviving vars and a removed-vars
migration table; its "promote to block" runbook named two variables that no
longer exist. Also swept: CLAUDE.md hook table, scanner-reference, ci-cd-guide,
both lethal-trifecta example docs, mitigation-matrix, injection-research.

Test counts in README/CLAUDE.md synced 2034 -> 2045.

Suite 2045 tests, 0 fail (2039 + 4 posture-trifecta + 2 riskScoreV1). The two
known parallel-load flakes did not recur this run.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BB4vXvwvtW4dxbPRd6vsez

docs/scanner-reference.md

@@ -27,7 +27,7 @@ AST-taint (AST) shells out to a PARSE-ONLY python3 helper (`scanners/lib/py-ast-
 Utility: `node scanners/lib/fs-utils.mjs <backup|restore|cleanup|tmppath> [args]`.
 
 Lib: `sarif-formatter.mjs` — converts scan output to OASIS SARIF 2.1.0 format. Used by `--format sarif` flag.
-Lib: `audit-trail.mjs` — writes structured JSONL audit events (ISO 8601, OWASP tags, SIEM-ready). Env: `LLM_SECURITY_AUDIT_*`.
+Lib: `audit-trail.mjs` — writes structured JSONL audit events (ISO 8601, OWASP tags, SIEM-ready). Enabled by the `audit.log_path` key in `.llm-security/policy.json` (v8.0.0; was `LLM_SECURITY_AUDIT_LOG`).
 Lib: `policy-loader.mjs` — reads `.llm-security/policy.json` for distributable hook configuration. Includes `ci` section (`failOn`, `compact`) for CI/CD defaults. Defaults match hardcoded values.
 
 **Standalone (8):** `posture-scanner.mjs` — deterministic posture assessment, 16 categories (incl. EU AI Act, NIST AI RMF, ISO 42001), <50ms. NOT in scan-orchestrator (meta-level, not code-level).