WS-E convergence: import SDK canonical label constants (eval vs controller-graph weight; gated on #175)

[bdchatham]

Follow-up to the WS-E SDK landing (sei-k8s-controller#421). seictl's seinode package re-declares the sei.io/role=node / sei.io/seinetwork label constants locally (pinned to the controller's values by a drift test). The SDK is now the canonical home for these.

Decision needed (not a mechanical swap):

• Importing github.com/sei-protocol/sei-k8s-controller/sdk/sei for the constants pulls the full controller module graph (controller-runtime, reconcilers) into seictl — heavy for a CLI.
• This is the accepted tradeoff of landing the SDK in the controller repo, and it's exactly what the api/ leaf-module split (sei-k8s-controller#175) would lighten.

Options to evaluate:

• Keep seictl's local constants + drift test (status quo; zero new dep weight) — possibly the right call for a CLI.
• After feat(sidecar): gov-vote handler (PR-B of #163) #175 lands, import a lightweight constants package from the SDK/api leaf module.

Gated on / informed by sei-k8s-controller#175. Tracked from the WS-E xreview ledger.