fix: add submodule checkout to pre-release workflow

The CI checkout step was missing submodules: recursive, causing
MokoSuiteClient to be an empty gitlink during builds. This resulted
in broken MokoSuiteClient.zip and "Install path does not exist" errors.

Claude-Session: https://claude.ai/code/session_01MbEjBtsSjPuTWhqqrMS2wG

.mokogitea/workflows/pre-release.yml

@@ -59,6 +59,13 @@ jobs:
           fetch-depth: 0
           token: ${{ secrets.MOKOGITEA_TOKEN }}
           ref: ${{ github.ref_name }}
+          submodules: recursive
+
+      - name: Update submodules to main
+        run: |
+          if [ -f .gitmodules ]; then
+            git submodule foreach 'git checkout main && git pull origin main' 2>/dev/null || true
+          fi
 
       - name: Setup mokocli tools
         env: