AuthStore.initialize() cleared the stored token on any error from
`api.getMe()`, which meant a transient failure — backend rolling
restart, network blip, HMR-aborted fetch in local dev — would force
a re-login. On 401 the token is already cleared upstream via
ApiClient.onUnauthorized, so the store's catch block only needs to
reset the in-memory user state.
Check `err instanceof ApiError && err.status === 401` before clearing
workspace context; leave the token in storage for every other error
so the next initialize() can retry.
Adds regression tests covering the 401 / 500 / network-failure / happy
paths.
