The 5h window reset time displayed for Setup Token accounts was inaccurate
because UpdateSessionWindow predicted the window end as "current hour + 5h"
instead of reading the actual `anthropic-ratelimit-unified-5h-reset` response
header. This caused the countdown to differ from the official Claude page.
Backend: parse the reset header (Unix timestamp) and use it as the real
window end, falling back to the hour-truncated prediction only when the
header is absent. Also correct stale predictions when a subsequent request
provides the real reset time.
Frontend: add a reactive 60s timer so the reset countdown in
UsageProgressBar ticks down in real-time instead of freezing at the
initial value.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
