v0.8.4

Fixed

• Silent auth failures now visible in dashboard — when OAuth tokens expire, the UI shows an auth banner and "Stale — poll failing" on usage gauges instead of silently displaying stale 0% data for hours.
• Respect Retry-After header on 429 rate-limit responses — avoids hammering the API when rate-limited.
• Service restart no longer kills itself on Windows.

Improved

• Dashboard polls auth status every 60s as a fallback, so persistent failures are always surfaced even after page refresh or SSE reconnect.
• /api/usage response now includes last_poll_at and poll_error fields for programmatic staleness detection.