feat: enhance markdown rendering

Adds remark-breaks for newline-to-br conversion and a custom
remarkSplitBlocks plugin to split paragraphs at hard breaks. Code blocks
over 15KB are truncated with a 'Show all' toggle for better
performance.

app/plugins/remark.ts

@@ -1,16 +1,59 @@
 import { unified } from 'unified';
+import { visit } from 'unist-util-visit';
 import remarkParse from 'remark-parse';
 import remarkGfm from 'remark-gfm';
 import remarkRehype from 'remark-rehype';
+import remarkBreaks from 'remark-breaks';
 import remarkMath from 'remark-math';
 import rehypeKatex from 'rehype-katex';
 
+function remarkSplitBlocks() {
+    return (tree: any) => {
+        visit(tree, 'paragraph', (node, index, parent) => {
+            const breakIndex = node.children.findIndex((child: any) => child.type === 'break');
+
+            if (breakIndex !== -1) {
+                const beforeBreak = node.children.slice(0, breakIndex);
+                const afterBreak = node.children.slice(breakIndex + 1);
+
+                node.children = beforeBreak;
+
+                const newParagraph = {
+                    type: 'paragraph',
+                    children: afterBreak,
+                };
+
+                let rootChildIndex = -1;
+                if (parent.type === 'root') {
+                    rootChildIndex = index!;
+                } else {
+                    rootChildIndex = tree.children.findIndex((child: any) =>
+                        child === parent || (child.children && child.children.includes(node))
+                    );
+
+                    if (rootChildIndex === -1) {
+                        rootChildIndex = tree.children.indexOf(parent);
+                    }
+                }
+
+                if (rootChildIndex !== -1) {
+                    tree.children.splice(rootChildIndex + 1, 0, newParagraph);
+                }
+
+                return index! + 1;
+            }
+        });
+    };
+}
+
 export default defineNuxtPlugin((nuxtApp) => {
     const remark =
         unified()
             .use(remarkParse)
             .use(remarkGfm)
             .use(remarkMath)
+            .use(remarkBreaks)
+            .use(remarkSplitBlocks)
             .use(remarkRehype, { allowDangerousHtml: true })
             .use(rehypeKatex, { output: 'mathml' });