Feature docs landing revamp

[xrissoula]

Description

This PR revamps the Polykey documentation home page (located under the "Getting Started" category) to improve its clarity and usefulness for new users. The changes include:

• Removing outdated or distracting elements (such as the divio system reference, which was removed in PK-Docs 1.0).
• Enhancing the high-level overview to better describe Polykey’s capabilities, including both the CLI and client library.
• Updating the encryption algorithms section: replacing the AES-GCM information with details on how Polykey now uses XChaCha20-Poly1305 for encryption.
• Structuring content into key sections such as introduction, quick start guide, documentation overview (Tutorials, How-To Guides, Theory, References), high-level use cases, and conclusion.

Issues Fixed

• Fixes Revamp Polykey Documentation Home Page #96

Tasks

• Remove unnecessary references (e.g., divio system mention) from the home page.
• Update the content and structure of the home page to include a high-level overview of Polykey, its capabilities, and relevant documentation sections.
• Update the encryption algorithm documentation to accurately reflect that Polykey uses XChaCha20-Poly1305 instead of AES-GCM.
• Gather additional team feedback and iterate on further enhancements as needed.

Final checklist

• Domain specific tests
• Full tests
• Updated inline-comment documentation
• Lint fixed
• Squash and rebased
• Sanity check the final build

[aryanjassal]

Perhaps we can add another section somewhere useful for recovering the agent. For example, @faithveloro09 had an issue where she was trying to recover her agent using a recovery code, but we haven't documented it anywhere, so I had to dig in the code a bit and try experimenting on a dummy node to figure out how it works. This should be better documented.

Key information:

• Recovery codes are 24 words long
• They need to be written to a file via a text editor instead of a word processing software like word, etc.
• To review the file contents, run the command cat <filename> and confirm the only content is the 24 word string and no other junk
• Use the --recovery-file-path flag (not sure about the name, needs confirming) to allow you to reset the agent password

@xrissoula You should try doing this yourself with a dummy node. Create a temporary node using --node-path like polykey agent start --node-path dummy-node-path and try recovering it to understand how the flow works. After you're done testing, you can remove the dummy-node-path directory.

[CMCDragonkai]

I thought the other PR already closed #96. So...? What's this about?

Not closing those issues means we aren't keeping tempo. @xrissoula

[aryanjassal]

I thought the other PR already closed #96. So...? What's this about?

Not closing those issues means we aren't keeping tempo. @xrissoula

You might be remembering #87. The previous issue was mostly to add a quick start guide and update the commands to what we now have. This one is cleaning up the landing page, the one you first see when you open polykey docs.

[xrissoula]

@aryanjassal @faithveloro09

i just fixed some commits today and also some formatting errors. all checks have passed now and the formatting is good. Ready to merge, i just am not allowed to do so myself.

[aryanjassal]

I've rebased the commits so the history looks cleaner. I also re-introduced the frontmatter header which shows the navigation sidebar on the left. Not sure why it was removed.

Otherwise it looks good. Merging.

[CMCDragonkai]

Review all silly mistakes and make notes on avoiding them.