fish: add theme function

fish/completions/theme.fish

@@ -0,0 +1,2 @@
+complete -f -c theme -n "not __fish_seen_subcommand_from dark light" -a "dark" -d "Set dark theme"
+complete -f -c theme -n "not __fish_seen_subcommand_from dark light" -a "light" -d "Set light theme"

fish/functions/theme.fish

@@ -0,0 +1,15 @@
+function theme
+    if test (count $argv) -eq 1
+        if test "$argv[1]" = "dark"
+            fish_config theme choose "Catppuccin Frappe"
+        else if test "$argv[1]" = "light"
+            fish_config theme choose "Catppuccin Latte"
+        else
+            echo "Error: Invalid theme. Use 'dark' or 'light'." >&2
+            return 1
+        end
+    else
+        echo "Usage: theme [dark|light]" >&2
+        return 1
+    end
+end