GitLab

- Add compile-time interface assertion for sessionWindowMockRepo
- Fix flaky fallback test by capturing time.Now() before calling UpdateSessionWindow
- Replace stale hardcoded timestamps with dynamic future values
- Add millisecond detection and bounds validation for reset header timestamp
- Use pause/resume pattern for interval in UsageProgressBar to avoid idle timers on large lists
- Fix gofmt comment alignment
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

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>