web: Fix inline documentation rendering (#13379)

web: Fix issues surrounding markdown rendering.

- Fix issue where Mermaid diagrams do not render.
- Fix link colors in dark mode.
- Fix anchored links triggering router.
- Fix issue where links occasionally link to missing page.

web/scripts/esbuild/remark/remark-links.mjs

@@ -0,0 +1,59 @@
+/**
+ * @import {Plugin} from 'unified'
+ * @import {} from 'mdast-util-directive'
+ * @import {} from 'mdast-util-to-hast'
+ * @import {Root, Link} from 'mdast'
+ * @import {VFile} from 'vfile'
+ */
+import * as path from "node:path";
+import { visit } from "unist-util-visit";
+
+const DOCS_DOMAIN = "https://goauthentik.io";
+
+/**
+ * Remark plugin to process links
+ * @type {Plugin<[unknown], Root, VFile>}
+ */
+export const remarkLinks = () => {
+    return function transformer(tree, file) {
+        const docsRoot = path.resolve(file.cwd, "..", "website");
+
+        /**
+         * @param {Link} node
+         */
+        const visitor = (node) => {
+            node.data = node.data || {};
+
+            if (node.url.startsWith("#")) {
+                node.data.hProperties = {
+                    className: "markdown-heading",
+                };
+
+                return;
+            }
+
+            node.data.hProperties = {
+                ...node.data.hProperties,
+                rel: "noopener noreferrer",
+                target: "_blank",
+            };
+
+            if (node.url.startsWith(".") && file.dirname) {
+                const nextPathname = path.resolve(
+                    "/",
+                    path.relative(docsRoot, file.dirname),
+                    node.url,
+                );
+                const nextURL = new URL(nextPathname, DOCS_DOMAIN);
+
+                // Remove trailing .md and .mdx, and trailing "index".
+                nextURL.pathname = nextURL.pathname.replace(/(index)?\.mdx?$/, "");
+
+                node.data.hProperties.href = nextURL.toString();
+            }
+        };
+
+        // @ts-ignore - visit cannot infer the type of the visitor.
+        visit(tree, "link", visitor);
+    };
+};