Add helper for paginating any Prisma query using a cursor derived from a configurable sort field

[Chucks1093]

Summary

Cursor pagination is implemented independently in each list endpoint with slightly different sort field handling. A generic paginateQuery<T>(model, where, orderBy, cursorField, limit, cursor?) helper should centralise the pattern and guarantee consistent cursor behaviour across all list endpoints.

Scope

• Add paginateQuery accepting a Prisma model delegate, where clause, orderBy, cursor field name, limit, and optional decoded cursor value
• Returns { items: T[], nextCursor: string | null, hasMore: boolean }
• Encode the cursor as base64 of JSON.stringify({ field, value }) for opacity
• Add unit tests: first page with no cursor, subsequent page using returned cursor, last page returns hasMore: false and nextCursor: null
• Replace inline pagination logic in at least two existing list endpoints with the helper

Acceptance Criteria

• First page returned correctly with no cursor
• Subsequent page uses returned cursor correctly
• Last page returns hasMore: false and nextCursor: null
• Cursor is opaque base64 string
• At least two existing endpoints use the helper

ETA: 12 hours

---

Coordinate on Telegram