chore(index.astro): fix typos, phrasing, punctuation

[andretchen0]

Just cleaning up a few typos and punctuation inconsistencies on the landing page.

In particular:

• Change variations of "ThreeJS" -> "Three.js"
• Change "vue" -> "Vue"
• Removed periods from titles, when they were present. (This seems to be the same policy Vue uses for their docs, as far as I can see.)
• Inserted periods if they were missing after complete sentences in body text. (Unless an emoji was used at the end of the sentence.)

I also changed my handle on the "procedural synthwave" demo.

(FWIW, I couldn't get the project to display without error as long as <SponsorSection /> was in index.astro. I removed the section while developing, but then added it back in the last commit.)

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