feat: enhance install script and theme generation

- install.sh now installs all variants when run without parameters
- preserve single-variant mode when --variant is specified
- add variant names to generated file headers for clarity
- fix tool name extraction to preserve compound names like git-delta
- fix CSS variable preservation during header generation

web/css/everforest-light-medium.css

@@ -1,4 +1,4 @@
-/* Everforest CSS Variables and Utility Classes */
+/* Everforest light-medium theme */
 /* Generated from template - do not edit manually */
 
 :root {