fix: update deprecated substituteInPlace syntax (#421)

- Change --replace to --replace-fail in plasma-manager-options.nix
- Update both options.md and manual.md substitutions
- Maintain same substitution behavior but use supported syntax

This removes usage of deprecated substituteInPlace --replace flag.

docs/plasma-manager-options.nix

@@ -28,12 +28,12 @@ stdenv.mkDerivation {
     cp ${./static/style.css} out/style.css
 
     substituteInPlace options.md \
-      --replace \
+      --replace-fail \
       '@OPTIONS_JSON@' \
       ${plasma-manager-options}/share/doc/nixos/options.json
 
     substituteInPlace manual.md \
-      --replace \
+      --replace-fail \
       '@VERSION@' \
       ${revision}