feat(consensus/keys): add keys import and keys export

[leninmehedy]

Summary

Third PR in the stacked series for epic #1164 — Consensus Node Key & Secret Management. Stacked on #1197 (base branch 01166-consensus-keys-generate).

Adds typed Kubernetes Secret I/O and the import / export verbs, turning a folder of key material into the per-node secrets the solo-operator consumes (and back).

What's in it

• kube client — ApplySecret (server-side apply; key bytes stay in memory, no temp file rendered) and GetSecretData.
• internal/consensus/keys — Import builds the three per-node secrets from a folder; Export writes them back to a folder for backup. Each key secret is named by the key's own date and fingerprint: node<N>-gossip-keys-<date>-<fp8>, node<N>-grpc-tls-keys-<date>-<fp8>, node<N>-admin-pubkey-<fp8>, with neutral, index-free inner-keys. <date> is the certificate's Not before date (so reimporting the same folder after a cluster reset gives the same names) and <fp8> is the start of its SHA-384. New key material therefore creates new secrets beside the old ones and never replaces them. Each secret carries solo.hiero.org/node, key-type and cert-fingerprint labels plus SHA-384 and not-after annotations (see feat(consensus/keys): name key secrets by key date and fingerprint; stage rotations beside live keys #1282).
• consensus keys import — --keys-dir, --source folder (vault tracked in feat(consensus/keys): ESO/vault source for 'keys import' #1171), --force, --gossip/--tls/--admin; --node-id required.
• consensus keys export — --keys-dir, selectors; --node-id required.

Custody & safety invariants

• import --secret-suffix <text> replaces the date part; export takes --fingerprint / --secret-suffix to choose one generation, and checks each secret's content against its name, so a renamed or edited secret is refused.
• import --label key=value (repeatable) puts extra labels on every secret, for example a reference to an external system (example.com/external-ref=ticket-42). Kubernetes label syntax applies and weaver's own labels (solo.hiero.org/node, key-type, cert-fingerprint) are reserved. When a secret's content is already up to date, only its labels are patched: the key data is never sent again, so it cannot be overwritten.
• Only the admin public key (admin.pub) is imported — the admin private key (admin.key) is never read or pushed to the cluster.
• The admin secret holds the public key as raw bytes (32 for Ed25519, 33 for compressed secp256k1), because solo-operator hex-encodes the secret value itself when it builds genesis. import decodes the hex in admin.pub; export writes it back as hex. Storing the hex text would double-encode the key in genesis-network.json. Operator follow-up: hashgraph/solo-operator#1394 proposes accepting hex text too.
• The gossip signing secret is the node's network identity, so a re-import is refused unless --force is passed.
• Export cannot recover the admin private key (it isn't in the cluster).

Join flow this enables

keys generate (node-id-free) → submit nodeCreate off-cluster → network assigns the node-id → keys import --node-id <assigned> → consensus node install. solo-provisioner never submits the DAB transaction.

Files

File	Purpose
internal/kube/client.go	ApplySecret (SSA) + GetSecretData
internal/kube/secret_test.go	GetSecretData tests
internal/consensus/keys/secrets.go	SecretClient iface, SecretNamesFor, Import/Export
internal/consensus/keys/secrets_test.go	import/export orchestration tests
cmd/cli/commands/consensus/keys/import.go	import subcommand
cmd/cli/commands/consensus/keys/export.go	export subcommand
cmd/cli/commands/consensus/keys/keys.go	selector/namespace/node-id helpers; wiring; stubbable client
cmd/cli/commands/consensus/keys/import_export_test.go	command tests
docs/commands/consensus.md	import + export sections

Testing

Validated in the UTM VM:

go test -race -cover ./pkg/consensus/keys/... ./internal/consensus/keys/... ./internal/kube/... ./cmd/cli/commands/consensus/keys/...

All pass. The ApplySecret server-side-apply happy path is exercised via the orchestration tests (the fake dynamic client cannot create through SSA) and by UAT against a real cluster.

Closes #1167.

[swirlds-automation]

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