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>

packages/api/src/router/audit-log.ts

@@ -49,10 +49,27 @@ export const auditLogRouter = createTRPCRouter({
         ];
       }
 
+      // Default to last 30 days if no date filter to avoid full table scan
+      if (!startDate && !endDate && !entityId) {
+        const thirtyDaysAgo = new Date();
+        thirtyDaysAgo.setDate(thirtyDaysAgo.getDate() - 30);
+        where.createdAt = { ...(where.createdAt as Record<string, Date> ?? {}), gte: thirtyDaysAgo };
+      }
+
       const items = await ctx.db.auditLog.findMany({
         where,
-        include: {
+        select: {
+          id: true,
+          entityType: true,
+          entityId: true,
+          entityName: true,
+          action: true,
+          userId: true,
+          source: true,
+          summary: true,
+          createdAt: true,
           user: { select: { id: true, name: true, email: true } },
+          // Exclude 'changes' from list query — fetch on demand when expanding
         },
         orderBy: { createdAt: "desc" },
         take: limit + 1,
@@ -68,6 +85,18 @@ export const auditLogRouter = createTRPCRouter({
       return { items, nextCursor };
     }),
 
+  /**
+   * Get a single audit entry with full changes JSONB (for expand/detail view).
+   */
+  getById: controllerProcedure
+    .input(z.object({ id: z.string() }))
+    .query(async ({ ctx, input }) => {
+      return ctx.db.auditLog.findUniqueOrThrow({
+        where: { id: input.id },
+        include: { user: { select: { id: true, name: true, email: true } } },
+      });
+    }),
+
   /**
    * Get all audit entries for a specific entity (e.g. a project or resource).
    */