docs: scaffold Tutorials tab and write enroll-a-remote-node

Adds the Tutorials tab to docs.json with 15 stub pages across three
groups (Fleet & nodes, Deploy & automate, Secure & integrate), and
writes the first full tutorial: enrolling a remote node via Pilot
Agent mode, verified end to end against a live control instance and
a second host running an existing Jellyfin Compose stack.

docs/tutorials/connect-a-git-source.mdx

@@ -0,0 +1,26 @@
+---
+title: Connect a Git Source
+sidebarTitle: Connect a Git source
+description: Step-by-step instructions for connecting a Git repository as a compose source.
+---
+
+<Note>
+  This tutorial is a placeholder pending full content. See the [Git Sources feature page](/features/git-sources) for the current reference documentation.
+</Note>
+
+## What you'll do
+
+## Prerequisites
+
+<Steps>
+  <Step title="">
+  </Step>
+</Steps>
+
+## Related
+
+<CardGroup cols={2}>
+  <Card title="Git Sources" icon="code-branch" href="/features/git-sources">
+    Sync compose files from a Git repository.
+  </Card>
+</CardGroup>