TBv3: Fix ungraceful 24-hour session expiry redirect

[jamlung-ri]

Summary

When an OCL session token expires (after ~24 hours), the user is not smoothly redirected back to their original destination. Instead they hit a confusing multi-step redirect — the app shows "back to application," then drops them at the home page with no indication of what happened.

Current Behavior

1. User is working in TBv3 with an active session
2. Token expires (after ~24 hours)
3. User attempts any authenticated action
4. App surfaces a confusing redirect prompt
5. After completing the auth flow, user is dropped at the home page — not returned to where they were

Expected Behavior

1. Session expires during active use
2. User is prompted to re-authenticate (cleanly, with context — e.g., "Your session has expired. Please log in to continue.")
3. After successful login, user is returned to the exact page/URL they were on before expiry

Notes

• The only related prior work is ocl_issues#2219 (CheckAuth.jsx), which added a loading spinner to suppress the 401 flash during the initial page load auth check. That does not address the mid-session token expiry redirect problem.
• This is a v3 MVP requirement: new users hitting this for the first time will perceive it as broken behavior.