perf: optimize Activity Log — lazy diff, 30-day default, getById

- List query: exclude changes JSONB from select (only metadata)
- Default to last 30 days when no date filter (avoids full table scan)
- New getById query: fetches full changes JSONB on demand
- ExpandedDiff component: fetches diff only when user expands an entry
- 5-minute staleTime on expanded diffs (cacheable, rarely changes)

Co-Authored-By: claude-flow <ruv@ruv.net>

apps/web/src/components/admin/ActivityLogClient.tsx

@@ -122,6 +122,28 @@ function DiffView({ changes }: { changes: Changes }) {
   );
 }
 
+function ExpandedDiff({ entryId }: { entryId: string }) {
+  const { data, isLoading } = trpc.auditLog.getById.useQuery(
+    { id: entryId },
+    { staleTime: 300_000 },
+  );
+
+  if (isLoading) {
+    return (
+      <div className="border-t border-gray-100 px-4 py-3 dark:border-slate-700">
+        <div className="h-4 w-48 shimmer-skeleton rounded" />
+      </div>
+    );
+  }
+
+  const changes = parseChanges((data as any)?.changes);
+  return (
+    <div className="border-t border-gray-100 px-4 py-3 dark:border-slate-700">
+      <DiffView changes={changes} />
+    </div>
+  );
+}
+
 function SummaryCards({ summary }: { summary: { byEntityType: Record<string, number>; total: number } }) {
   const sorted = useMemo(() => {
     return Object.entries(summary.byEntityType)
@@ -355,7 +377,6 @@ export function ActivityLogClient() {
         )}
 
         {allEntries.map((entry) => {
-          const changes = parseChanges(entry.changes);
           const isExpanded = expandedId === entry.id;
           const entityLink = ENTITY_LINKS[entry.entityType]?.(entry.entityId);
 
@@ -431,12 +452,8 @@ export function ActivityLogClient() {
                 </svg>
               </button>
 
-              {/* Expanded Diff */}
-              {isExpanded && (
-                <div className="border-t border-gray-100 px-4 py-3 dark:border-slate-700">
-                  <DiffView changes={changes} />
-                </div>
-              )}
+              {/* Expanded Diff — fetched on demand */}
+              {isExpanded && <ExpandedDiff entryId={entry.id} />}
             </div>
           );
         })}