Revert "Remove mermaid-cli dependency"

This reverts commit ab27a23.

Author: josh

pkgs/LazyVim.nix

@@ -115,13 +115,11 @@ in
             "ERROR None of the tools found: 'trash', 'gio', 'kioclient5', 'kioclient'"
             "ERROR is not ready"
             "ERROR your terminal does not support the kitty graphics protocol"
-            "ERROR Tool not found: 'mmdc'"
             "WARNING Image rendering in docs with missing treesitter parsers won't work"
             "WARNING Missing Treesitter languages"
             "WARNING No system trash command found; deleting files will be permanent"
             "WARNING The `latex` treesitter parser is required to render LaTeX math expressions"
             "WARNING dashboard did not open: `headless`"
-            "WARNING `mmdc` is required to render Mermaid diagrams"
             "WARNING setup {disabled}"
           ];
         };

pkgs/tests/snacks-nvim-checkhealth.nix

@@ -11,12 +11,10 @@ callPackage ./neovim-checkhealth.nix {
     "ERROR None of the tools found: 'trash', 'gio', 'kioclient5', 'kioclient'"
     "ERROR is not ready"
     "ERROR your terminal does not support the kitty graphics protocol"
-    "ERROR Tool not found: 'mmdc'"
     "WARNING Image rendering in docs with missing treesitter parsers won't work"
     "WARNING Missing Treesitter languages"
     "WARNING No system trash command found; deleting files will be permanent"
     "WARNING The `latex` treesitter parser is required to render LaTeX math expressions"
-    "WARNING `mmdc` is required to render Mermaid diagrams"
     "WARNING setup {disabled}"
     "WARNING {which-key} is not installed"
   ];

plugins.nix

@@ -20,6 +20,7 @@
   gzip,
   imagemagick,
   lazygit,
+  mermaid-cli,
   nodePackages,
   nodejs_24,
   php83,
@@ -227,6 +228,7 @@ let
         ghostscript
         imagemagick
         lazygit
+        mermaid-cli
         tectonic
       ];
     };