feat: switch theme to risotto and update config

- Add risotto theme as submodule
- Update hugo.yaml with new theme configuration
- Adjust menu URLs to be absolute paths
- Simplify makefile by removing redundant prep steps
- Update copyright notice and author info
- Remove old theme-specific CSP settings

.gitmodules

@@ -1,3 +1,6 @@
 [submodule "themes/hugo-coder"]
 	path = themes/hugo-coder
 	url = https://github.com/luizdepra/hugo-coder.git
+[submodule "themes/risotto"]
+	path = themes/risotto
+	url = https://github.com/joeroe/risotto