[1/2] feat: accept generation model catalogues

[dazzatronus]

Studio cannot offer generation models without a catalogue, and hardcoding one would tie every model launch to an SDK release. Registration now takes an optional snapshot of the expanded GET /models?expand=options response and normalises it into the shapes the editor can work with. Nothing renders yet — that is [2/2].

Decisions a reviewer cannot see in the diff:

• A snapshot, not a subscription. No fetching, refresh, billing or pricing logic enters the SDK; the published pricing block is ignored.
• Entries without an options schema are dropped, because an unexpanded entry and a model with genuinely no options are indistinguishable.
• Models whose schema requires inputSrc are excluded — source media has no picker in this release.
• Reconciliation keeps a raw merge-field placeholder when its resolved value is valid, so switching models never destroys one.
• The only new public surface is the optional catalogue; the UI bridge is @internal and stripped from dist/index.d.ts.

Verify: npm run verify:ci

Risk: none at runtime — a stored catalogue with no reader.

[github-actions]

🎉 This PR is included in version 2.18.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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