Fix Cursor plan percent calculation

[Hilo-Hilo]

Summary

• Fix Cursor plan percent calculation by using used + remaining (fallback: limit) instead of plan.breakdown.total.
• Prevents Cursor from incorrectly showing 0% left when breakdown fields reflect used spend.

Test plan

• ./Scripts/compile_and_run.sh
• Verified via CodexBarCLI usage --provider cursor (Cursor Ultra now reports ~60% remaining instead of 0%).

[ratulsarna]

Thanks for the PR! We merged #240, which fixes the Cursor plan percent/limit bug by using plan.limit instead of breakdown.total. This PR now conflicts because it touches the same lines, so I’m going to close it as superseded. If you’ve seen real payloads where plan.limit is missing/incorrect but remaining is present (making used + remaining the right denominator), please comment with a redacted /api/usage-summary example and we can do a focused follow-up PR.