Clean up and restructure site

[google-labs-jules]

Cleaned up the Astro codebase by removing unused and junk files (about1.mdx, why_*, etc.). Restructured the events section by renaming events1 to events and pointing the navigation correctly. Separated "Events" (using projects collection) and "Blog" (using posts collection) in the navbar and updated page metadata accordingly. Fixed build warnings related to missing html tags in markdown pages.

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PR created automatically by Jules for task 3817522873110096499 started by @DarrenVictoria

[google-labs-jules]

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