🧹 Replace deprecated substr with substring in TranscriptViewer

[alfieprojectsdev]

🎯 What: Replaced the deprecated String.prototype.substr(14, 5) with String.prototype.substring(14, 19) in field-logic/src/components/TranscriptViewer.tsx.
💡 Why: substr is deprecated and not recommended for use. substring (or slice) is the standard alternative. This change improves code health and future compatibility.
✅ Verification:

• Extracted the timestamp formatting logic into a helper function formatTimestamp.
• Created a new unit test file field-logic/src/components/TranscriptViewer.test.ts to verify the logic.
• Ran tests with npx vitest run and confirmed they pass.
• Verified syntax with prettier.
  ✨ Result: The code is cleaner, follows modern standards, and is now testable.

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PR created automatically by Jules for task 4011063382388960841 started by @alfieprojectsdev

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