🧪 [testing improvement] Add tests for generateId in backfill-metadata.js

[akutuva21]

🎯 What: The testing gap addressed is the lack of unit tests for the generateId utility function in scripts/backfill-metadata.js, which handles constructing canonical IDs from file paths.

📊 Coverage: The following scenarios are now tested:

• Standard path structures.
• Filtering out specific excluded directory names (Published, Examples, Tutorials).
• Fallback behavior when all path segments are excluded.
• Replacing invalid characters (spaces, dashes) with underscores.

✨ Result: Test coverage for backfill-metadata.js is improved, ensuring the path parsing and ID generation logic is reliable and won't be easily broken during future refactoring.

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PR created automatically by Jules for task 12012714592641404061 started by @akutuva21

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