fix(ci): replace actions/checkout with git clone in docs workflow

The docs runner is a bare host without Node.js, so actions/checkout@v4
fails with 'Cannot find: node in PATH'. Replace with a plain git
fetch/checkout that works without Node.

.gitea/workflows/docs.yml

@@ -4,14 +4,21 @@ on:
   push:
     branches: [main]
     paths:
-      - 'docs/**'
+      - "docs/**"
+      - ".gitea/workflows/docs.yml"
 
 jobs:
   build-and-deploy:
     runs-on: docs
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        run: |
+          if [ -d .git ]; then
+            git fetch origin main
+            git checkout -f origin/main
+          else
+            git clone --depth 1 --branch main https://git.kindred-systems.com/kindred/create.git .
+          fi
 
       - name: Build mdBook
         run: mdbook build docs/