fix: stale feed data on refresh and viewer data loss after token expiry
Disable URL response caching on XRPC GET requests so pull-to-refresh
always hits the server. Make authContext() async to await token refresh
before returning, preventing requests with expired tokens that return
200 with null viewer data instead of triggering 401 retry.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>