feat: switch to biome, apply formatting, shellcheck (#227)

* feat: switch to biome, apply formatting, shellcheck
* chore: apply cr comments
* chore: few config tweaks, shellcheck hook now py-based
* chore: lint fixes and pr comments
* chore(lint): megalinter, and other fixes

Signed-off-by: Ismo Vuorinen <ismo@ivuorinen.net>

local/bin/dfm

@@ -25,6 +25,7 @@ source_file()
   case "$CURRENT_SHELL" in
     fish)
       if [[ -f "$file.fish" ]]; then
+        # shellcheck disable=SC1090
         source "$file.fish"
       else
         echo "Fish shell file not found: $file.fish"
@@ -32,6 +33,7 @@ source_file()
       fi
       ;;
     sh | bash | zsh)
+      # shellcheck disable=SC1090
       source "$file"
       ;;
     *)