Remove unsupported education source, add keywords, and fix formatting

[brikin01]

• Cleaned up embedding-generation/vector-db-sources.csv so every row follows the six-column schema and malformed comma-shifted rows parse correctly
• Removed unsupported education resource rows, mainly raw .pptx / .ipynb sources that the current parser could chunk poorly (support follow-up added as STESOL-542)
• Added keywords for transcript-backed education videos and remaining educational resource rows (thus fixing failing unit tests)
• Fixed visible encoding artifacts (e.g. μVision)

Support for chunking video transcript content will be done as part of STESOL-526

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Pull request overview

Copilot reviewed 1 out of 2 changed files in this pull request and generated 2 comments.

[NeethuESim]

LGTM