feat(client): render YAML frontmatter in markdown preview (full/diff)

docs/syntax-sample/frontmatter-array-after.md

@@ -0,0 +1,18 @@
+---
+title: 'Release Notes'
+tags:
+  - release
+  - v1.2.0
+authors:
+  - Alice
+  - Bob
+categories:
+  - update
+  - guide
+---
+
+## v1.2.0
+
+This release includes minor bug fixes and performance improvements.
+
+See the changelog for full details and migration notes.

docs/syntax-sample/frontmatter-array-before.md

@@ -0,0 +1,17 @@
+---
+title: 'Release Notes'
+tags: []
+authors:
+  - Alice
+  - Carol
+categories:
+  - guide
+  - update
+  - legacy
+---
+
+## v1.2.0
+
+This release includes minor bug fixes.
+
+See the changelog for full details.

docs/syntax-sample/frontmatter-nested-1-after.md

@@ -0,0 +1,16 @@
+---
+title: 'About the Team'
+seo:
+  title: 'About Us | Difit'
+  description: 'Learn about our team, mission, and values.'
+  noindex: false
+author:
+  name: 'Jane Smith'
+  email: 'jane@example.com'
+---
+
+## Our Story
+
+We started as a small group of enthusiasts back in 2020.
+
+Today we are a growing team dedicated to open source software.

docs/syntax-sample/frontmatter-nested-1-before.md

@@ -0,0 +1,16 @@
+---
+title: 'About the Team'
+seo:
+  title: 'About Us'
+  description: 'Learn about our team and mission.'
+author:
+  name: 'Jane Doe'
+  email: 'jane@example.com'
+  bio: 'Loves open source.'
+---
+
+## Our Story
+
+We started as a small group of enthusiasts.
+
+Today we are a growing team dedicated to open source.

docs/syntax-sample/frontmatter-nested-deep-after.md

@@ -0,0 +1,18 @@
+---
+title: 'Site Configuration'
+site:
+  name: 'Difit Docs'
+  seo:
+    meta:
+      title: 'Difit Documentation | Guides'
+      description: 'Official documentation for difit.'
+      og:
+        image: '/images/og-cover.png'
+        type: 'website'
+---
+
+## Configuration Overview
+
+This page describes the site-wide configuration options available to maintainers.
+
+Update these values when rebranding or relaunching the documentation site.

docs/syntax-sample/frontmatter-nested-deep-before.md

@@ -0,0 +1,16 @@
+---
+title: 'Site Configuration'
+site:
+  name: 'Difit Docs'
+  seo:
+    meta:
+      title: 'Difit Documentation'
+      og:
+        image: '/images/og-default.png'
+---
+
+## Configuration Overview
+
+This page describes the site-wide configuration options.
+
+Update these values when rebranding the documentation site.

docs/syntax-sample/frontmatter-scalar-after.md

@@ -0,0 +1,14 @@
+---
+date: 2026-01-15
+weight: 10
+published: false
+title: 'Getting Started Guide'
+category: 'tutorial'
+description: 'A short guide for new users.'
+---
+
+## Introduction
+
+This guide walks you through the basic setup process.
+
+Follow the steps below to get your development environment ready before diving into advanced topics.

docs/syntax-sample/frontmatter-scalar-before.md

@@ -0,0 +1,14 @@
+---
+title: 'Getting Started'
+date: '2026-01-10'
+published: true
+draft: false
+weight: '10'
+description: null
+---
+
+## Introduction
+
+This guide walks you through the basic setup process.
+
+Follow the steps below to get your environment ready.

package.json

@@ -69,6 +69,7 @@
     "commander": "^15.0.0",
     "diff": "^9.0.0",
     "express": "^5.1.0",
+    "js-yaml": "^4.3.0",
     "lucide-react": "^1.0.0",
     "mermaid": "^11.13.0",
     "open": "^11.0.0",
@@ -90,6 +91,7 @@
     "@testing-library/user-event": "^14.6.1",
     "@tsconfig/strictest": "^2.0.5",
     "@types/express": "^5.0.3",
+    "@types/js-yaml": "^4.0.9",
     "@types/node": "^24.0.8",
     "@types/react": "^19.1.8",
     "@types/react-dom": "^19.1.6",