[chronik-docs] Fix broken links

Summary: And restore the API reference navigation.

Test Plan:
First pnpm install and build ecashaddrjs
Second pnpm install chronik-client
Then:

pnpm --filter ecashaddrjs install
pnpm --filter ecashaddrjs run build
pnpm --filter chronik-client install
pnpm --filter chronik-docs install
pnpm --filter chronik-docs run build
pnpm --filter chronik-docs run serve

Or run the docker build.

Reviewers: #bitcoin_abc, bytesofman

Reviewed By: #bitcoin_abc, bytesofman

Subscribers: bytesofman

Differential Revision: https://reviews.bitcoinabc.org/D19146