refactor: pricing

[harshiv-26]

Note

Medium Risk
Large catalog-wide pricing metadata change; wrong or divergent pricing vs costs could affect billing if consumers switch to the new field before validation is complete.

Overview
Introduces a service-tier pricing model on ModelConfig: optional pricing with standard and priority keys, each holding the same region-scoped cost entries as legacy costs. The Cue schema (#Pricing, #ServiceTiers) and generated OpenAPI/TS types are updated; costs stays in place but is marked deprecated for backward compatibility.

Across many provider YAMLs (ai21, anthropic, aws-bedrock, etc.), each touched model gains a pricing.standard block that mirrors existing costs (including multi-region Bedrock entries, cache/batch fields, and tiered long-context pricing where present). Legacy costs is not removed in this diff.

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