fix keycloak session timeout errors

[chloe-yuu]

1. Replace generic “Failed to fetch” errors with clear session-expiration messages to prevent the screen from appearing frozen.
2. Implement periodic Keycloak token refresh (every 240 seconds) to avoid token expiry and extend the effective session duration from 5 minutes to 30 minutes.

[sonarqubecloud]

Quality Gate failed

Failed conditions
0.0% Coverage on New Code (required ≥ 80%)
B Reliability Rating on New Code (required ≥ A)

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