fix(csi): prefer target lvol device after failover

[boddumanohar]

Fixes #537

Summary

• preserve the existing model-first device lookup for ordinary volumes
• when the backend returns targetLvolID, prefer the target clone identity before stale model coordinates
• add a regression test for the C6 stale-source/model-vs-target selection case

Verification

• red first: go test ./internal/initiator -run TestMatchNamespaceDevicePrefersTargetLvolOverStaleModel -count=1 -v failed because the model link was selected
• green: go test ./internal/initiator -run 'TestMatchNamespaceDevicePrefersTargetLvolOverStaleModel|TestMatchNamespaceDevicePrefersModelOverLvol|TestMatchNamespaceDeviceFallbackNeedsNsidSuffix' -count=1 -v\n- green: go test ./internal/initiator -count=1\n- green: go test ./internal/...\n- green: .claude/skills/house-style/scripts/quality-gate.sh --changed\n\n## Notes\n- go test ./... in csi-driver was started but stopped after several minutes without output beyond the first package; the narrower ./internal/... suite completed successfully.\n- The C6 mechanism was also verified on the configured cluster using block-mode disposable PVCs. No full replication failover was performed because the cluster had no replication pair/op resources available.\n