fix(presets/genesis-chain): opt validators into sidecar signing via operatorKeyring

[bdchatham]

Summary

• Add `operatorKeyring: {}` to the bench validator template in the `genesis-chain` preset. Without it, sei-k8s-controller emits no `SEI_KEYRING_BACKEND` on the sidecar, the Cosmos SDK can't open any keyring, and gov-vote / gov-software-upgrade tasks fail their preconditions.
• With the empty block, the controller wires the sidecar with `SEI_KEYRING_BACKEND=test` + `SEI_KEYRING_DIR=$SEI_HOME/keyring-test` — exactly where the gentx task writes the validator key during the genesis ceremony. The sidecar reads it back and gov-vote / gov-software-upgrade unlock for nightly major-upgrade workflows.

Depends on

• fix(noderesource): wire SEI_KEYRING_BACKEND; add gentx-key fallback path sei-k8s-controller#296 (must merge first)

Test plan

• `go test ./nodedeployment/...` passes (preset is YAML; tests load it as-is).
• End-to-end: nightly major-upgrade workflow on harbor cluster signs gov-vote + gov-software-upgrade tasks successfully after both this PR and the controller PR land.

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[bdchatham]

Superseded — the preset opt-in is no longer needed. Per cross-review (sei-protocol/sei-k8s-controller#296), the controller now defaults validators to a test-backend keyring rooted at $SEI_HOME (the SDK appends keyring-test/), removing the need for an explicit operatorKeyring: {} block on the preset. Replaced by #186 (rename gentx uid to node_admin) which fixes the actual blocker (key uid mismatch between gentx and the sidecar's signing flow).