Update CI and docs to use submodules for maiko/notecards/loops/test

doHCFILES.yml: replace 5 separate checkout steps with a single
  checkout using submodules:true; remove now-redundant .git cleanup step.

buildLoadup.yml: add submodules:true to Checkout Medley; remove
  separate Checkout Notecards + tar steps (notecards.tgz was already
  commented out of the release push).

make-gh-pages.md: replace manual clone+copy instructions with
  git clone --recurse-submodules; remove rm -rf of submodule dirs.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.github/workflows/doHCFILES.yml

@@ -51,33 +51,8 @@ jobs:
 
       - name: Checkout Medley repo
         uses: actions/checkout@v4
-
-      - name: Checkout maiko
-        uses: actions/checkout@v4
         with:
-          repository: ${{ github.repository_owner }}/maiko
-          path: ./maiko
-
-      - name: Checkout notecards
-        uses: actions/checkout@v4
-        with:
-          repository: ${{ github.repository_owner }}/notecards
-          path: ./notecards
-
-      - name: Checkout loops
-        uses: actions/checkout@v4
-        with:
-          repository: ${{ github.repository_owner }}/loops
-          path: ./loops
-
-      - name: Checkout test
-        uses: actions/checkout@v4
-        with:
-          repository: ${{ github.repository_owner }}/test
-          path: ./test
-
-      - name: Cleanup .git for notecards, loops, test
-        run: rm -rf ./notecards/.git ./loops/.git ./test/.git
+          submodules: true
 
       - name: Download Maiko
         run: |