feat(audit): add pricing signature guards and reporting

Add snapshot, signature, and drift guard support for Vertex AI, Cloudflare Workers AI, and Perplexity API, backed by a queryable audit table and recent-window view.

This commit also wires the audit query layer into daily signal materialization and report generation so structure drift becomes a first-class signal instead of a log-only artifact.

scripts/cloudflare_pricing_snapshot_lib.go

@@ -0,0 +1,24 @@
+//go:build llm_script
+
+package main
+
+import "time"
+
+var cloudflarePricingSignatureContainsNeedles = map[string]string{
+	"llm":             "llm",
+	"pricing":         "pricing",
+	"cf_model_prefix": "@cf/",
+	"price_tokens":    "price in tokens",
+}
+
+func buildCloudflarePricingStructureSignature(raw string) markdownPricingStructureSignature {
+	return buildMarkdownPricingStructureSignature(raw, cloudflarePricingSignatureContainsNeedles)
+}
+
+func writeCloudflarePricingSnapshotArtifacts(raw string, sourceURL string, snapshotPath string, signaturePath string, now time.Time) (markdownPricingStructureSignature, error) {
+	return writeMarkdownPricingSnapshotArtifacts(raw, sourceURL, snapshotPath, signaturePath, now, cloudflarePricingSignatureContainsNeedles)
+}
+
+func resolveCloudflarePricingSnapshotPaths(snapshotPath string, signaturePath string, snapshotDir string, now time.Time) (string, string) {
+	return resolveMarkdownPricingSnapshotPaths(snapshotPath, signaturePath, snapshotDir, "cloudflare-pricing", now)
+}