feat: lift praxis theme CSS into sass entry point

- main.scss imports the praxis theme partial
- Fix missing semicolon at line 1836 that SCSS strict mode rejected
- Bootstrap and mobile-menu remain separate <link> tags (loaded from /css/)

sass/main.scss

@@ -0,0 +1,8 @@
+// Praxis am Lienhardplatz — theme entry point
+//
+// Compiled by Zola into /main.css and loaded by base.html.
+// Bootstrap, mobile-menu, flexslider, and Font Awesome are loaded as separate
+// <link> tags from /css/ (see templates/partials/head.html), so we don't import
+// them here. Only the praxis-specific theme styles compile through SASS.
+
+@import "praxis_theme";