chore: bump cosmos-sdk to v0.500.0 final

[tbruyelle]

Summary

Bumps the cosmos-sdk fork from the release candidate to the final v0.500.0 tag, the last dependency blocking the v4.0.0 release.

Note: The SDK final bump was part of #343 originally, but only that PR's first commit (ibc-go v10.7.0 / Go 1.26.4 / module security bumps) landed on main — the SDK commit did not. This PR re-applies it on top of current main.

Changes

• go.mod: cosmos-sdk => atomone-hub/cosmos-sdk v0.500.0-rc3 → v0.500.0.
• x/coredaos/keeper/hooks.go: the final SDK added AfterConsensusPubKeyUpdate(ctx, oldPk, newPk, fee) to the StakingHooks interface (validator consensus pubkey rotation). x/coredaos is the only StakingHooks implementer in the repo; implemented as a no-op, consistent with the module's other non-delegation hooks.

⚠️ Reviewer note: the final SDK enabling consensus pubkey rotation likely introduces new staking params (rotation fee, max rotations). Confirm whether the v4 upgrade handler needs to initialize them — RunMigrations runs the staking migration, but any chain-specific non-default values must be set explicitly in the handler.

Verification

• go build ./... ✅
• go test ./x/... ./ante/... ./post/... ./app/... ✅
• govulncheck ./... → No vulnerabilities found ✅

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