Reduce bold font overuse in svd_intro lecture

[jstac]

Summary

Closes #792 — the svd_intro lecture's "The Setting" section (section 5.2) overuses bold formatting, with 11 bold phrases across ~13 sentences and "singular value decomposition" bolded 3 times repeatedly.

This PR reduces the bold count in that section from 11 to 6 by:

• Removing bold from "data" (line 37): A common term that doesn't need typographic emphasis.
• Removing bold from "patterns" (line 55): A common term that doesn't need emphasis in context.
• Removing bold from "singular value decomposition" (lines 55, 59): Already bolded on first use in the section (line 51); repeating the bold on subsequent mentions adds visual noise without aiding comprehension.
• Removing bold from "principal components analysis" (line 55): Already introduced with bold in the Overview section (line 25).

Bold is preserved for:

• First-use introductions of key terms: individual, random variable, short and fat, tall and skinny, singular value decomposition (first occurrence)
• dynamic mode decomposition — its first appearance in the body text

Principle applied

Bold only on first introduction of a term; avoid re-bolding terms the reader has already encountered.

Test plan

• Verify the rendered lecture reads naturally without excessive emphasis
• Confirm key terms are still bolded on first use for discoverability

🤖 Generated with Claude Code

[github-actions]

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Commit: 66b8259

📚 Changed Lectures

• svd_intro

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Build Info

• Workflow: Build Project [using jupyter-book]