restore redirects from vitepress transition

[dckc]

971 is progress on migrating to vitepress; there's remaining work to restore some redirects. Perhaps we should land vitepress in the interest of getting fulltext search etc. and track the redirects separately.

IOU:

• [ ] what's the impact, exactly? how many redirects? how likely are folks to run into them?

cc @0xpatrickdev @gibson042

[0xpatrickdev]

c69ed8a may close this. See comment: https://github.com/Agoric/documentation/pull/971#discussion_r1525311846