Update to new networking API shape, with IPv6

[charliepark]

This PR updates console to work with the new API shape for IP pool selection introduced in oxidecomputer/omicron#9598.

Still have a few decisions to make in terms of forms / UI.

A note for the eventual review:

Scenario	defaultPool	Behavior
No unicast defaults	undefined	Uses { type: 'ephemeral' } (API picks pool)
One unicast default (v4 or v6)	Pool name	Uses explicit pool: { poolSelector: { type: 'explicit', pool } }
Dual defaults (v4 + v6)	undefined	Uses auto with version: { poolSelector: { type: 'auto', ipVersion } }
Multicast defaults only	undefined	Uses { type: 'ephemeral' } (ignored correctly)

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Project	Deployment	Review	Updated (UTC)
console	Ready	Preview	Jan 23, 2026 7:10am