docs: Improve docs with core-concept and guides

apps/wiki/lib/cn.ts

@@ -0,0 +1 @@
+export { twMerge as cn } from 'tailwind-merge';

apps/wiki/lib/get-llm-text.ts

@@ -0,0 +1,10 @@
+import {source} from '@/lib/source';
+import type {InferPageType} from 'fumadocs-core/source';
+
+export async function getLLMText(page: InferPageType<typeof source>) {
+  const processed = await page.data.getText('processed');
+
+  return `# ${page.data.title} (${page.url})
+
+${processed}`;
+}