feat(security): prefer digest identity in scan history (#1610)

Retain scans and History search by digest when available, keep imageRefLike for compatibility, and surface digests in compare.

frontend/src/lib/formatDigest.ts

@@ -0,0 +1,10 @@
+/**
+ * Shorten a Docker content digest or image ID for display.
+ * Accepts `sha256:…` or bare hex; returns up to 12 hex characters.
+ */
+export function formatShortDigest(id: string | null | undefined): string {
+  if (!id) return '';
+  const colon = id.indexOf(':');
+  const hex = colon >= 0 ? id.slice(colon + 1) : id;
+  return hex.slice(0, 12);
+}