feat: add comprehensive DOCX document support

- Install docx (v9.5.1) and mammoth (v1.11.0) packages
- Create docxService.ts with full DOCX read/write functionality:
  - Extract text, HTML, and Markdown from DOCX files using mammoth
  - Generate DOCX files from Markdown with proper heading levels (H1-H3)
  - Generate DOCX files from HTML and plain text
  - Automatic paragraph formatting and spacing
- Integrate DOCX conversions into pandocService.ts
- Update README with DOCX support documentation
- Add DOCX libraries to tech stack section

Supported DOCX conversions:
- DOCX → Text/HTML/Markdown
- Markdown/HTML/Text → DOCX

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

lib/converters/pandocService.ts

@@ -8,6 +8,14 @@ import {
   htmlToPDF,
   plainTextToPDF,
 } from './pdfService';
+import {
+  docxToText,
+  docxToHTML,
+  docxToMarkdown,
+  textToDOCX,
+  markdownToDOCX,
+  htmlToDOCX,
+} from './docxService';
 
 // Import DOMPurify only on client side
 let DOMPurify: any;
@@ -53,6 +61,20 @@ export async function convertWithPandoc(
       }
     }
 
+    // Handle DOCX conversions
+    if (inputExt === 'docx') {
+      // DOCX input
+      if (outputFormat === 'txt') {
+        return await docxToText(file, onProgress);
+      } else if (outputFormat === 'html') {
+        return await docxToHTML(file, onProgress);
+      } else if (outputFormat === 'md' || outputFormat === 'markdown') {
+        return await docxToMarkdown(file, onProgress);
+      } else {
+        throw new Error(`Conversion from DOCX to ${outputFormat} not supported`);
+      }
+    }
+
     // Handle conversions TO PDF
     if (outputFormat === 'pdf') {
       if (inputExt === 'md' || inputExt === 'markdown') {
@@ -66,6 +88,19 @@ export async function convertWithPandoc(
       }
     }
 
+    // Handle conversions TO DOCX
+    if (outputFormat === 'docx') {
+      if (inputExt === 'md' || inputExt === 'markdown') {
+        return await markdownToDOCX(file, onProgress);
+      } else if (inputExt === 'html' || inputExt === 'htm') {
+        return await htmlToDOCX(file, onProgress);
+      } else if (inputExt === 'txt') {
+        return await textToDOCX(file, onProgress);
+      } else {
+        throw new Error(`Conversion from ${inputExt} to DOCX not supported`);
+      }
+    }
+
     // Perform conversion based on input and output formats
     if (inputExt === 'md' || inputExt === 'markdown') {
       // Markdown input