fix: group-by sticky pagination not rendering for virtual relationship fields (#14470)

### What?

Fixes pagination when grouping by virtual relationship fields in
collection list views. The sticky pagination toolbar now correctly
appears when there are 10+ distinct values, and `totalPages` is
calculated accurately.

### Why?

When grouping by virtual relationship fields (e.g.,
`virtualTitleFromCategory` with `virtual: 'category.title'`), the
pagination was broken:
- `totalPages` always returned `1` even when there were 10+ distinct
values
- The sticky pagination toolbar at the bottom never appeared

This happened because:
1. The recursive `findDistinct` call for virtual fields wasn't passing
through `limit` and `page` parameters
2. MongoDB's count aggregation pipeline was missing the relationship
`$lookup` stages needed to traverse virtual field paths

### How?

**1. Fixed recursive findDistinct call**
- Added `limit` and `page` parameters to the recursive call when
handling virtual fields

**2. Fixed MongoDB count aggregation**
- Changed count pipeline to include the same stages as the main query
(`sortAggregation`, `relationLookup`, `$unwind`, `$group`)
- Ensures relationship lookups are performed before counting distinct
values

Author: PatrikKozak

packages/db-mongodb/src/findDistinct.ts

@@ -215,22 +215,31 @@ export const findDistinct: FindDistinct = async function (this: MongooseAdapter,
       $skip: (page - 1) * args.limit,
     })
     pipeline.push({ $limit: args.limit })
-    const totalDocs = await Model.aggregate(
-      [
-        {
-          $match: query,
-        },
-        {
-          $group: {
-            _id: `$${fieldPath}`,
-          },
-        },
-        { $count: 'count' },
-      ],
+
+    // Build count pipeline with the same structure as the main pipeline
+    // to ensure relationship lookups are included
+    const countPipeline: PipelineStage[] = [
       {
-        session,
+        $match: query,
       },
-    ).then((res) => res[0]?.count ?? 0)
+      ...(sortAggregation.length > 0 ? sortAggregation : []),
+      ...(relationLookup?.length ? relationLookup : []),
+      ...($unwind
+        ? [
+            {
+              $unwind,
+            },
+          ]
+        : []),
+      {
+        $group,
+      },
+      { $count: 'count' },
+    ]
+
+    const totalDocs = await Model.aggregate(countPipeline, {
+      session,
+    }).then((res) => res[0]?.count ?? 0)
     const totalPages = Math.ceil(totalDocs / args.limit)
     const hasPrevPage = page > 1
     const hasNextPage = totalPages > page

packages/payload/src/collections/operations/findDistinct.ts

@@ -174,8 +174,10 @@ export const findDistinctOperation = async (
         depth: args.depth,
         disableErrors,
         field: path,
+        limit: args.limit,
         locale,
         overrideAccess,
+        page: args.page,
         populate,
         req,
         showHiddenFields,