chore: opportunity for monorepo-wide dead code cleanup with knip

npx knip reports a large amount of potentially removable dead code across the monorepo (~357 unused files, ~83 unused dependencies, ~64 unused devDependencies on current master [my local is a dozen commits behind but it around this area]).

From my experience using knip on other repositories, unused dependencies tend to have false positives but unused files are usually pretty accurate.

To validate, I picked a random file that it flagged: apps/www/components/BackedBy.tsx (~3 years old). Global search for BackedBy returns no imports/usages outside the file itself. The commit f26761121a is the commit that removed the last invocation of the BackedBy component.

Knip was added in #35072 and there has been recent studio-focused cleanup (#47122, #47387, #47399), but there doesn't appear to be a tracking issue for monorepo-wide dead code removal especially outside apps/studio.

I think there's significant cleanup opportunity in apps/www, apps/docs, apps/design-system, etc.), much of it likely leftover from App Router / component migrations.