Add Scale Engineer newsletter embed to visualizer content pages

[RohitLakh]

Summary

• Add a reusable NewsletterEmbed that loads the Scale Engineer subscribe iframe (with theme + UTM params).
• Place the newsletter embed in the content sidebar across visualizer pages—above Daily DSA where it exists, and as a standalone sidebar on linked list / tree content pages.
• Fix horizontal overflow on small screens by replacing invalid w-100 dividers with w-full.
• Slightly increase Daily DSA embed iframe height for better fit.

Proof:

Without Daily DSA Embed

With Daily DSA Embed

[vercel]

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