chore: relax RelatedAsset validation and filter invalid assets

[zone-live]

Explanation

Fixes a production bug where one relatedAsset missing sourceAssetId caused the entire What's Happening section to show an error state.

• Make name and sourceAssetId optional in RelatedAssetStruct
  and RelatedAsset type (symbol is now the only required field)
• Replace normalizeRelatedAssets with filterAndNormalizeRelatedAssets
  which strips assets with empty symbol and drops trends with zero
  valid assets after filtering

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

Medium Risk
Changes public types and validation for market-overview related assets; clients must handle optional name/sourceAssetId, but behavior aligns with live API and reduces full-section failures.

Overview
Relaxes market overview RelatedAsset validation so partially enriched API rows no longer fail the whole response.

RelatedAsset.name and RelatedAsset.sourceAssetId are now optional in the superstruct schema (RelatedAssetStruct) and the exported RelatedAsset type; symbol remains required. Missing name or sourceAssetId no longer causes fetchMarketOverview to throw API_INVALID_RESPONSE. JSDoc now tells clients to fall back to symbol when name is absent.

Tests were updated: invalid-entry cases focus on a missing symbol, and new cases assert successful overviews when sourceAssetId or name is omitted. The changelog documents the fix under Unreleased → Fixed.

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