fix: move mermaid script to before_closing_body_tag for proper rendering (#289)

Mermaid diagrams were rendering as code blocks instead of images because
the script was loaded in the head tag before the DOM content was available.
Moving to `before_closing_body_tag` ensures the script runs after all
page content is loaded, allowing mermaid to find and transform the code
blocks.

Closes #287

Author: jimsynz

mix.exs

@@ -57,13 +57,7 @@ defmodule Reactor.MixProject do
           before_closing_head_tag: fn type ->
             if type == :html do
               """
-              <script src="https://cdn.jsdelivr.net/npm/[email protected]/dist/mermaid.min.js"></script>
               <script>
-                mermaid.initialize({
-                  startOnLoad: true,
-                  theme: 'default'
-                });
-                
                 if (location.hostname === "hexdocs.pm") {
                   var script = document.createElement("script");
                   script.src = "https://plausible.io/js/script.js";
@@ -75,6 +69,19 @@ defmodule Reactor.MixProject do
               """
             end
           end,
+          before_closing_body_tag: fn type ->
+            if type == :html do
+              """
+              <script src="https://cdn.jsdelivr.net/npm/[email protected]/dist/mermaid.min.js"></script>
+              <script>
+                mermaid.initialize({
+                  startOnLoad: true,
+                  theme: 'default'
+                });
+              </script>
+              """
+            end
+          end,
           groups_for_modules: [
             Dsl: ~r/^Reactor\.Dsl.*/,
             Steps: ~r/^Reactor\.Step.*/,