docs(reference/nix-daemon-protocol): migrate

This moves the daemon protocol reference to the "Reference" section in
our new docs.

It also updates them a bit, we now use `{{< relref "path/to/file.md" >}}`
to refer to other files, and fixes the (previously broken) references
in handshake.md.

Change-Id: I114e40622dc504e7a5f75946895900e797a1e722
Reviewed-on: https://cl.snix.dev/c/snix/+/30273
Autosubmit: Florian Klink <flokli@flokli.de>
Tested-by: besadii
Reviewed-by: Brian Olsen <brian@maven-group.org>

web/content/docs/reference/nix-daemon-protocol/intro.md

@@ -0,0 +1,25 @@
+---
+title: Intro
+slug: Intro
+description: ""
+summary: ""
+date: 2025-03-24T13:10:37+02:00
+lastmod: 2025-03-24T13:10:37+02:00
+draft: false
+weight: 50
+toc: true
+---
+
+The Nix Daemon protocol is what's used to communicate with the `nix-daemon`,
+either on the local system (in which case the communication happens via a Unix
+domain socket), or with a remote Nix (in which this is tunneled over SSH).
+
+It uses a custom binary format which isn't too documented. This reference here
+aims to serve as an in-depth documentation about some of the inner workings,
+data types etc.
+
+A first implementation of this exists in
+[griff/Nix.rs](https://github.com/griff/Nix.rs/tree/main).
+
+Work is underway to port / factor this out into reusable building blocks into
+the [nix-compat](https://snix.dev//rustdoc/nix_compat/index.html) crate.