fix: surface vuln_scanning across licence, staff and pricing UI

The catalogue row alone was not enough; the feature was invisible in
three places and mislabelled in a fourth.

PlanConfigurator rendered every key that was not "console" as "Single
sign-on", so the staff checkbox granting vulnerability scanning was
labelled single sign-on. Feature wording was duplicated between the staff
configurator and the purchase form and the copies had drifted, so it now
lives in adminsite/lib/features.ts and both read from it.

The customer licence panel showed raw keys; it now labels them.

Pricing gains a comparison row. The add-on block with a monthly price is
deliberately NOT added: that is a pricing decision, and the Paddle price
IDs for the new catalogue rows have to be pasted in before it can be sold
anyway.

adminsite/lib/features.ts

@@ -0,0 +1,27 @@
+/* Human wording for licence feature keys.
+ *
+ * One place, because there were two and they disagreed: the staff configurator
+ * rendered every key that was not "console" as "Single sign-on", so adding a
+ * third feature silently mislabelled the checkbox that grants it. A map with a
+ * fallback degrades to the raw key, which is ugly but never wrong.
+ *
+ * Keys must match shared/license/license.go. */
+export const FEATURE_LABEL: Record<string, string> = {
+    console: "Browser console",
+    oidc: "Single sign-on",
+    vuln_scanning: "Vulnerability scanning",
+};
+
+export const FEATURE_DESC: Record<string, string> = {
+    console: "In-browser SSH, RDP and VNC sessions",
+    oidc: "OIDC sign-in for your whole team",
+    vuln_scanning: "Package inventory matched against distribution security advisories",
+};
+
+export function featureLabel(key: string): string {
+    return FEATURE_LABEL[key] ?? key;
+}
+
+export function featureDesc(key: string): string {
+    return FEATURE_DESC[key] ?? "";
+}