test(utils): add coverage for attestation-CSV and PNG-export helpers (#1976)

[s6pa1rta3n-lab]

Summary

Closes #1976.

Restores src/utils/chartExport.ts and adds comprehensive unit test coverage in src/utils/__tests__/chartExport.test.ts for attestation CSV export helpers and PNG export functions with DOM and canvas mocking:

• Attestation CSV Export Helpers:

  • buildAttestationCsvRows: covers ISO string conversion for Date instances and pass-through for pre-formatted strings, as well as mixed inputs.
  • buildAttestationCsvContent: verifies header row inclusion, field formatting, formula-injection character escaping (=, +, -, @), and empty array handling.
  • buildAttestationExportFilename: verifies filename sanitization and fallback to 'commitment' on empty input ID.
  • ATTESTATION_CSV_HEADERS: validates all 6 standard export columns.

• PNG Export Functions:

  • loadImage: validates resolution on successful image loading and rejection on load error.
  • exportSvgElementToPng: tests error paths for missing 2D canvas context (Canvas context unavailable), failed PNG blob generation (Failed to create PNG blob), and image loading failure (Failed to load chart SVG for PNG export). Also verifies successful blob generation and download triggering, including auto-injection of missing xmlns attributes.
  • exportChartContainerToPng: tests error path when svg.recharts-surface is missing (Chart SVG not found) and successful export delegation when present.

Payout Stipulations Checklist

• Restore src/utils/chartExport.ts with all required export symbols.
• Extend src/utils/__tests__/chartExport.test.ts to test buildAttestationCsvRows with both Date and string timestamps.
• Test formula escaping and empty array handling in buildAttestationCsvContent.
• Test filename sanitization and empty ID fallback in buildAttestationExportFilename.
• Test PNG export error paths (Canvas context unavailable, Chart SVG not found, Failed to create PNG blob, image load failure) using DOM and canvas mocks.
• Pass all unit tests and achieve 100% test coverage for chartExport.ts.
• Zero linting or code formatting errors.
• Self-documenting code with JSDoc docstrings and no inline comments.

Payout Routing

• EVM (Base/Arbitrum/Polygon/ETH): 0xF46C9F6d70C50BF81ef3588AB523a90a594a2F89
• Stellar: GCL6OXAMLD75BMTINA6EMRUDWK5THQUSHMYNLSNBCJAPZJHNYJTUNIBC

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