feat: apply Noto Serif font and heading styles to DOCX export

Add document-level styles so the downloaded .docx has:
- Noto Serif font throughout (matching the web UI)
- Sized headings: H1 20pt, H2 16pt, H3 14pt, H4 12pt
- 11pt body text with 1.15× line spacing
- Consistent color (#1f1b16) and spacing
- Styled hyperlinks (blue, underlined)
- List paragraph font inheritance

Co-Authored-By: alex <alex@semipublic.co>

src/markdownToDocx.js

@@ -197,6 +197,82 @@ export function markdownToDocx(markdown, title) {
 
   return new Document({
     title: title || 'PMC Funding Brief',
+    styles: {
+      default: {
+        document: {
+          run: {
+            font: 'Noto Serif',
+            size: 22, // 11 pt
+            color: '1f1b16',
+          },
+          paragraph: {
+            spacing: { after: 160, line: 276 }, // 1.15× line spacing
+          },
+        },
+        heading1: {
+          run: {
+            font: 'Noto Serif',
+            size: 40, // 20 pt
+            bold: true,
+            color: '1f1b16',
+          },
+          paragraph: {
+            spacing: { before: 360, after: 120 },
+          },
+        },
+        heading2: {
+          run: {
+            font: 'Noto Serif',
+            size: 32, // 16 pt
+            bold: true,
+            color: '1f1b16',
+          },
+          paragraph: {
+            spacing: { before: 300, after: 120 },
+          },
+        },
+        heading3: {
+          run: {
+            font: 'Noto Serif',
+            size: 28, // 14 pt
+            bold: true,
+            color: '1f1b16',
+          },
+          paragraph: {
+            spacing: { before: 240, after: 80 },
+          },
+        },
+        heading4: {
+          run: {
+            font: 'Noto Serif',
+            size: 24, // 12 pt
+            bold: true,
+            color: '1f1b16',
+          },
+          paragraph: {
+            spacing: { before: 200, after: 80 },
+          },
+        },
+        listParagraph: {
+          run: {
+            font: 'Noto Serif',
+            size: 22,
+          },
+        },
+      },
+      paragraphStyles: [
+        {
+          id: 'Hyperlink',
+          name: 'Hyperlink',
+          run: {
+            color: '1d4ed8',
+            underline: { type: 'single' },
+            font: 'Noto Serif',
+            size: 22,
+          },
+        },
+      ],
+    },
     numbering: {
       config: [
         {