Deploy the sidereus7 submodule at /sidereus7/

The submodule was registered but never checked out in CI, so its
content was silently absent from every deploy. Check out submodules
during the Pages build, and move the submodule's path from
sidereus7.github.io to sidereus7 so Jekyll copies it straight to the
URL path we want.

Renaming only the path (not the submodule name) leaves .git/modules
alone, so existing clones just need `git submodule sync`.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TyCX1VdE3hpgadJbhPhFCH

Author: claude

.github/workflows/jekyll-gh-pages.yml

@@ -28,6 +28,9 @@ jobs:
     steps:
       - name: Checkout
         uses: actions/checkout@v4
+        with:
+          # Pull in the sidereus7 submodule; Jekyll copies it to /sidereus7/.
+          submodules: recursive
       - name: Setup Pages
         uses: actions/configure-pages@v5
       - name: Build with Jekyll

.gitmodules

@@ -1,3 +1,3 @@
 [submodule "sidereus7.github.io"]
-	path = sidereus7.github.io
+	path = sidereus7
 	url = https://github.com/ddrcoder/sidereus7.github.io