Use Home root nav without top tabs (#43)

## Summary
- set explicit root nav label to Home
- remove navigation.tabs so top-level tab nav is not shown on Home

---------

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Author: MariusStorhaug

.github/zensical.toml

@@ -2,6 +2,9 @@
 site_name = "-{{ REPO_NAME }}-"
 repo_name = "-{{ REPO_OWNER }}-/-{{ REPO_NAME }}-"
 repo_url = "https://github.com/-{{ REPO_OWNER }}-/-{{ REPO_NAME }}-"
+nav = [
+  {"Home" = "index.md"},
+]
 
 [project.theme]
 language = "en"