SEO: Fix broken backlinks

Some pages across the web were linking to the blog in ways that would return 404. This PR updates and restructures how redirects work for the blog, with the goal of the redirecting, using Vercel rules, to support 3 basic usecases:

Requests to /research or /writings should redirect to the front page
Requests to /research/:slug or /writings/:slug should strip the first section and redirect to /:slug
Requests to /the-cost-of-resiliencea redirect to /the-cost-of-resilience - this is apparently a common broken URL found in the wild, and the SEO guide suggests setting up the redirect to not lose the SEO power

Using Vercel rules means better support for correct HTTP status codes, so we no longer need the useRedirect custom component, which has been removed.

Task: Broken Backlinks

Following the SEO guide here: https://docs.google.com/spreadsheets/d/13Xa_TKfuKrWzrK0zCgJNnQPXFK95hiBxqnLWE7cvHN8/edit#gid=1086684444

flashbots / flashbots-writings-website

SEO: Fix broken backlinks #160