feat(admin-cli): Add Domain creation command

[kfelternv]

Adds nico-admin-cli domain create --name <name> so operators can create a DNS Domain through the existing Core CreateDomain RPC and see the created Domain in the configured output format. Domain deletion and REST exposure remain out of scope while their reference and ownership rules are decided.

Related issues

• feat: expose Domain (DNS zone) creation/deletion and NetworkSegment VPC/subdomain linkage via REST API and Go SDK #4371

Type of Change

• Add - New feature or capability
• Change - Changes in existing functionality
• Fix - Bug fixes
• Remove - Removed features or deprecated functionality
• Internal - Internal changes (refactoring, tests, docs, etc.)

Breaking Changes

• This PR contains breaking changes

Testing

• Unit tests added/updated
• Integration tests added/updated
• Manual testing performed
• No testing required (docs, internal refactor, etc.)

Additional Notes

• cargo test --locked -p nico-admin-cli (235 passed)
• cargo clippy --locked -p nico-admin-cli --all-targets --all-features -- -D warnings
• cargo carbide-lints -p nico-admin-cli --all-targets --all-features --locked
• cargo +nightly-2026-06-16 fmt --all -- --check
• Exercised domain create --help and the missing---name parser error

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