Estimator, blog, changelog, and a live community card

A batch of additions focused on conversion, content, and proof.

- Added an interactive price estimator in a popup, with a live total
- Added the blog at /blog (MDX writeups)
- Added this changelog at /changelog
- Added a live Discord card on the homepage with an online count
- New custom 404 page with built-in site search

Housekeeping:

- Moved FAQ out of the top nav (still on the homepage)