feat(documents): entity-aggregated query params + signing-details API

GET /api/v1/files?entityType=client&entityId=… and the same params on
the documents route return the owner-aggregated projection
{ groups: [{ label, source, files|workflows, total }] }. folderId
remains for direct-folder listing; the two modes are mutually
exclusive (zod refine).

GET /api/v1/documents/[id]/signing-details returns
{ workflow, signers, events } for the "view signing details" dialog
on signed-PDF rows.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/app/api/v1/files/route.ts

@@ -3,13 +3,23 @@ import { NextResponse } from 'next/server';
 import { withAuth, withPermission } from '@/lib/api/helpers';
 import { parseQuery } from '@/lib/api/route-helpers';
 import { errorResponse } from '@/lib/errors';
-import { listFiles } from '@/lib/services/files';
+import { listFiles, listFilesAggregatedByEntity } from '@/lib/services/files';
 import { listFilesSchema } from '@/lib/validators/files';
 
 export const GET = withAuth(
   withPermission('files', 'view', async (req, ctx) => {
     try {
       const query = parseQuery(req, listFilesSchema);
+
+      if (query.entityType && query.entityId) {
+        const result = await listFilesAggregatedByEntity(
+          ctx.portId,
+          query.entityType,
+          query.entityId,
+        );
+        return NextResponse.json({ data: result });
+      }
+
       const result = await listFiles(ctx.portId, query);
 
       const { page, limit } = query;