Add md2pdf: Markdown-to-PDF CLI with Finder Quick Action

- bin/md2pdf: converts .md to PDF via pandoc + headless Chrome
  (no LaTeX needed); writes alongside source, supports -o and --css
- bin/md2pdf.css: clean GitHub-style default stylesheet
- bin/md2pdf-install-quickaction: installs the Finder right-click action
- macos/md2pdf.workflow: version-controlled Quick Action bundle
  (right-click .md files to Convert to PDF)

macos/md2pdf.workflow/Contents/Info.plist

@@ -0,0 +1,32 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+<dict>
+	<key>NSServices</key>
+	<array>
+		<dict>
+			<key>NSMenuItem</key>
+			<dict>
+				<key>default</key>
+				<string>Convert to PDF (md2pdf)</string>
+			</dict>
+			<key>NSMessage</key>
+			<string>runWorkflowAsService</string>
+			<key>NSRequiredContext</key>
+			<dict>
+				<key>NSApplicationIdentifier</key>
+				<string>com.apple.finder</string>
+			</dict>
+			<key>NSSendFileTypes</key>
+			<array>
+				<string>net.daringfireball.markdown</string>
+				<string>public.plain-text</string>
+			</array>
+			<key>NSSendTypes</key>
+			<array>
+				<string>NSFilenamesPboardType</string>
+			</array>
+		</dict>
+	</array>
+</dict>
+</plist>