chore: pull in latest penumbra guide

[conorsch]

There were a few recent changes made to the guide in the protocol repo, as of [0], and this commit pulls those changes in. At the very least, I noticed that changes from the following PRs were missing:

• https://github.com/penumbra-zone/penumbra/pull/4732
• https://github.com/penumbra-zone/penumbra/pull/4726

Tried to make sure to preserve unique content updates implemented during the mdbook -> nextra conversion.

[0] https://github.com/penumbra-zone/penumbra/tree/a2ffd8a79f1b397e81df7b7e31b256d545cdf004/docs/guide

[github-actions[bot]]

Visit the preview URL for this PR (updated for commit 9fc96d0):

https://penumbra-guide--pr2-latest-penumbra-guid-62oqxkf2.web.app

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