chore: pass marketCap on Trade (social-trading)

[zone-live]

Explanation

Pass marketCap to Trade, meaning TradeStruct + Trade type get marketCap?: number | null..

References

Checklist

• I've updated the test suite for new or updated code as appropriate
• I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
• I've communicated my changes to consumers by updating changelogs for packages I've changed
• I've introduced breaking changes in this PR and have prepared draft pull requests for clients and consumer packages to resolve them

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Note

Low Risk
Backward-compatible optional field on trade validation/types only; no auth, persistence, or behavior changes.

Overview
Extends Trade / TradeStruct with an optional marketCap field (number | null) so consumers can show the token’s USD market cap at trade time when the social API (Clicker) provides it.

The superstruct schema in social-types.ts is updated and Trade is still derived via Infer, so any API responses that already validate trades through TradeStruct (e.g. position trades in SocialService) accept the new property without breaking older payloads that omit it. The package changelog records the addition under Unreleased.

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