Convert public directory from submodule to normal directory

- Remove public from git submodule tracking
- Add all public directory contents as regular files
- Fixes GitHub Actions error: "No url found for submodule path 'public' in .gitmodules"

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

public/book/1/ZGlkOnBsYzo0aHFqZm43bTZuNWhubzNkb2FtdWhnZWY/gitbook/gitbook-plugin-mermaid-gb3/book/plugin.js

@@ -0,0 +1,7 @@
+require([
+  'gitbook'
+], function (gitbook) {
+  gitbook.events.bind('page.change', function () {
+    mermaid.init();
+  });
+});