Describe provider contracts, references and public model facts

[softmarshmallow]

The catalogue can now describe model facts at their actual scope: native reference APIs, independent provider contracts, public regular prices, and official code/weights. All additions retain schema v1 and accept the existing catalogue unchanged.

• Sourced provider endpoints/parameters, capabilities, limits and token-price bands; explicit presentation-only reference_provider; reviewed coverage/absence/exclusion records across all families and rig-check.
• Public USD components with exact meters, conditions, ranges and rounding. Unknown pricing stays absent. Omitted upper bounds and no-rounding increments serialize losslessly through TOML.
• Published image-output calculators/examples and qualified vision-tokenization rules. Rounded USD examples are distinct from exact token estimates.
• Optional distribution URLs, exact weight variants, separate licenses and public/gated access. These do not imply a hosted API or inference permission.
• Validated source qualifications; regular non-promotional prices only. Documentation and skills distinguish public Grida service facts from private consumer policy and preserve existing model coverage.

Negative checks cover missing/malformed sources, duplicate variants, invalid bounds/conditions, non-JSON values, overlapping bands, invalid references, contradictory coverage and unsupported calculator examples. No provider registry or implicit routing default is introduced.

Validation: unchanged 61-card catalogue passes; 275 checker/release tests pass, pinned formatter and skill validation pass. Independent review completed and findings fixed. This PR contains schema/tooling/guidance only; sourced population is stacked in #12. No merge or release publication performed.