feat: add markdown-to-pdf converter with Puppeteer

Introduce a Node.js CLI tool that converts Markdown files to styled
PDFs using `marked` for parsing and `puppeteer` for rendering.

- Add `md-to-pdf.js` as the main conversion script with:
  - CLI argument handling for input/output file paths
  - Automatic output directory creation alongside the input file
  - Pre-processing to strip thematic breaks (`---`) before headings
  - Embedded CSS for clean, print-ready styling (headings, tables,
    code blocks, blockquotes, page breaks, etc.)
  - PDF generation via Puppeteer with A4 format and custom margins
- Add `.gitignore` to exclude `node_modules/` and `output/` directories
- Add `package-lock.json` with resolved dependencies (marked, puppeteer)

package.json

@@ -0,0 +1,21 @@
+{
+  "name": "markdown-to-pdf",
+  "version": "1.0.0",
+  "description": "",
+  "main": "index.js",
+  "scripts": {
+    "test": "echo \"Error: no test specified\" && exit 1"
+  },
+  "repository": {
+    "type": "git",
+    "url": "ssh://gitea@192.168.1.62/hykocx/markdown-to-pdf.git"
+  },
+  "keywords": [],
+  "author": "",
+  "license": "ISC",
+  "type": "commonjs",
+  "dependencies": {
+    "marked": "^18.0.0",
+    "puppeteer": "^24.40.0"
+  }
+}