### What?
Fixed groupBy functionality for polymorphic relationships, which was
throwing errors.
<img width="1099" height="996" alt="Screenshot 2025-09-11 at 3 10 32 PM"
src="https://github.com/user-attachments/assets/bd11d557-7f21-4e09-8fe6-6a43d777d82c"
/>
### Why?
The groupBy feature failed for polymorphic relationships because:
- `relationshipConfig` was undefined when `relationTo` is an array
(polymorphic)
- ObjectId serialization errors when passing database objects to React
client components
- hasMany relationships weren't properly flattened into individual
groups
- "No Value" groups appeared first instead of populated groups
### How?
- Handle polymorphic relationship structure `{relationTo, value}`
correctly by finding the right collection config using `relationTo`
- Add proper collection config lookup for each relation in polymorphic
relationships during populate
- Flatten hasMany relationship arrays so documents with `[Category1,
Category2]` create separate groups for each
---
- To see the specific tasks where the Asana app for GitHub is being
used, see below:
- https://app.asana.com/0/0/1211331842191589
9c20eb34d4