Invalidate stale pack cache with old packId format

The cache contained API responses with packId (old format) but the
new mapper produces id. The store read these from cache, bypassing
the API, and sortPacks filtered them out (no id field) → empty page.

Fix: readCache() now detects stale entries (packId present, id missing)
and clears them, forcing a fresh API fetch through the mapper.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/Web/StellaOps.Web/src/app/features/policy-studio/services/policy-pack.store.ts

@@ -98,7 +98,13 @@ export class PolicyPackStore {
       const raw = sessionStorage.getItem(this.cacheKey);
       if (!raw) return null;
       const parsed = JSON.parse(raw) as PolicyPackSummary[];
-      return Array.isArray(parsed) && parsed.length > 0 ? parsed : null;
+      if (!Array.isArray(parsed) || parsed.length === 0) return null;
+      // Reject stale cache entries that have packId instead of id (old API format)
+      if (!parsed[0].id && (parsed[0] as any).packId) {
+        sessionStorage.removeItem(this.cacheKey);
+        return null;
+      }
+      return parsed;
     } catch {
       return null;
     }