Lazy load journal and account report pages

[zhouwuji]

Summary

This PR improves performance for large journal and account journal pages by avoiding eager loading of all rows at once.

Changes

• add paginated journal loading for the main journal view
• add paginated loading for account report journal views
• return \ from the related API endpoints
• increase page size to 500 to reduce follow-up requests during scrolling

Motivation

Large ledgers and account journals can become slow when too many journal rows are transferred and rendered at once. This change moves the UI to incremental loading so the initial render stays lighter and subsequent pages are loaded on demand.

Notes

• this PR does not include the experimental Pretext-based virtualization work
• the goal here is to keep the change smaller and easier to review first

Testing

• tested locally against large journal and account pages
• verified incremental loading works when scrolling
• verified related JSON API responses include pagination metadata