bug: Silent error discards in credential persistence and config loading

[jflowers]

Summary

Several locations silently discard errors from credential persistence and configuration loading, making it difficult to diagnose authentication and config failures.

Affected Locations

1. Token persistence errors silently dropped

File: internal/auth/oauth.go:146-148

newJSON, _ := json.Marshal(newToken)  // marshal error dropped
_ = p.store.Set(secrets.KeyOAuthToken, string(newJSON))  // persist error dropped

If token persistence fails, the user will be forced to re-authenticate on every run with no diagnostic information.

2. Credential store write error dropped

File: cmd/gcal-organizer/auth_config.go:104

_ = store.Set(secrets.KeyClientCredentials, string(credsData))

If keychain write fails during auth login, user gets no indication credentials were not saved.

3. UserHomeDir errors dropped

File: cmd/gcal-organizer/main.go:99,129

home, _ := os.UserHomeDir()

If UserHomeDir fails, home is empty and migration runs against a relative path.

Fix

Add warning-level logging at each site:

if err := store.Set(...); err != nil {
    logging.Logger.Warn("failed to persist token to store", "error", err)
}

Priority

MEDIUM — Silent failures make credential issues very difficult to diagnose.