feat(api): add bill-history pagination

[khaira777]

Summary

The bill list endpoint applies a result limit but does not provide offset/cursor traversal, so clients cannot retrieve records after the first page.

Current behavior

main/routes/bills.ts:73-108 limits the list response but has no documented offset, cursor, or continuation token.

Expected behavior

Authorized clients should be able to traverse the complete bill history without duplicates or omissions.

Acceptance criteria

• Add documented cursor or offset pagination with stable ordering.
• Preserve existing filters, role checks, and response compatibility where possible.
• Add traversal tests across more than one page and boundary cases.

Relevant files

main/routes/bills.ts, bill history frontend consumers