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)

bin/md2pdf.css

@@ -0,0 +1,120 @@
+/* md2pdf default stylesheet — clean, GitHub-flavored, print-friendly. */
+
+@page {
+  margin: 2cm 1.9cm;
+}
+
+html {
+  font-size: 12pt;
+}
+
+body {
+  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Helvetica, Arial,
+    sans-serif;
+  line-height: 1.55;
+  color: #1f2328;
+  max-width: 46em;
+  margin: 0 auto;
+  padding: 0 0.5em;
+  -webkit-print-color-adjust: exact;
+  print-color-adjust: exact;
+  word-wrap: break-word;
+}
+
+/* --- Headings --- */
+h1, h2, h3, h4, h5, h6 {
+  margin-top: 1.4em;
+  margin-bottom: 0.5em;
+  font-weight: 600;
+  line-height: 1.25;
+}
+h1 { font-size: 1.9em; border-bottom: 1px solid #d1d9e0; padding-bottom: 0.3em; }
+h2 { font-size: 1.45em; border-bottom: 1px solid #d1d9e0; padding-bottom: 0.3em; }
+h3 { font-size: 1.2em; }
+h4 { font-size: 1em; }
+h5 { font-size: 0.9em; }
+h6 { font-size: 0.85em; color: #59636e; }
+h1:first-child, h2:first-child, h3:first-child { margin-top: 0; }
+
+/* Keep a heading with the content that follows it. */
+h1, h2, h3, h4, h5, h6 { break-after: avoid; }
+
+/* --- Body elements --- */
+p, ul, ol, dl, table, pre, blockquote { margin-top: 0; margin-bottom: 1em; }
+
+a { color: #0969da; text-decoration: none; }
+a:hover { text-decoration: underline; }
+
+strong { font-weight: 600; }
+
+ul, ol { padding-left: 2em; }
+li + li { margin-top: 0.25em; }
+li > ul, li > ol { margin-top: 0.25em; margin-bottom: 0; }
+
+/* --- Code --- */
+code, pre, kbd, samp {
+  font-family: ui-monospace, SFMono-Regular, "SF Mono", Menlo, Consolas,
+    "Liberation Mono", monospace;
+  font-size: 0.88em;
+}
+
+code {
+  background-color: rgba(129, 139, 152, 0.15);
+  padding: 0.2em 0.4em;
+  border-radius: 6px;
+}
+
+pre {
+  background-color: #f6f8fa;
+  border: 1px solid #d1d9e0;
+  border-radius: 6px;
+  padding: 1em;
+  overflow: auto;
+  line-height: 1.45;
+  break-inside: avoid;
+}
+pre code {
+  background: transparent;
+  padding: 0;
+  border-radius: 0;
+  font-size: 100%;
+  white-space: pre;
+}
+
+/* --- Blockquotes --- */
+blockquote {
+  margin-left: 0;
+  padding: 0 1em;
+  color: #59636e;
+  border-left: 0.25em solid #d1d9e0;
+}
+blockquote > :last-child { margin-bottom: 0; }
+
+/* --- Tables --- */
+table {
+  border-collapse: collapse;
+  width: 100%;
+  display: block;
+  overflow: auto;
+  break-inside: avoid;
+}
+th, td {
+  border: 1px solid #d1d9e0;
+  padding: 0.5em 0.85em;
+  text-align: left;
+}
+th { background-color: #f6f8fa; font-weight: 600; }
+tr:nth-child(2n) td { background-color: #f6f8fa; }
+
+/* --- Rules & images --- */
+hr {
+  height: 1px;
+  border: 0;
+  background-color: #d1d9e0;
+  margin: 1.8em 0;
+}
+
+img { max-width: 100%; box-sizing: border-box; }
+
+/* pandoc wraps the --metadata title in a header; keep it unobtrusive. */
+header#title-block-header h1.title { margin-bottom: 0.8em; }