When loadSession() fails during boot with a non-404 error (401, 400,
500, network), the session ID stays stuck in localStorage and the URL,
causing repeated failures on every page refresh.
The 404 path already had inline self-heal (clears localStorage + URL).
This extends it to all error cases:
- Added _clearStuckSessionOnBoot() helper to consolidate the self-heal
logic for non-404 errors.
- On 401 redirect (api() returns undefined): clears the stuck session
ID and shows a more informative message.
- On other non-404 errors: clears the stuck session ID and shows a
better error message distinguishing auth failures from other errors.
Preserves the guard that prevents clearing localStorage when clicking
into a *different* dead session while already viewing a healthy one.
3bca16fdc2
