Add public API documentation endpoint

Features:
- New GET /docs/api endpoint to retrieve full API documentation
- Returns API.md content as JSON with markdown format
- No authentication required (public endpoint)
- Includes lastUpdated timestamp
- 26,754 characters of complete documentation

Response format:
{
  "success": true,
  "documentation": "<full markdown content>",
  "format": "markdown",
  "lastUpdated": "2025-12-08T12:12:38.942Z"
}

Use case:
- Fetch documentation programmatically
- Display in external applications
- Copy-paste into AI assistants (Claude, ChatGPT)
- Auto-generate API clients

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

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

src/server.js

@@ -101,7 +101,7 @@ app.use((req, res, next) => {
 // API Authentication Middleware
 const authenticate = (req, res, next) => {
   // Skip authentication for public endpoints
-  const publicEndpoints = ['/health', '/api'];
+  const publicEndpoints = ['/health', '/api', '/docs/api'];
   // Allow public download endpoint
   if (publicEndpoints.includes(req.path) || req.path.startsWith('/public/download/')) {
     return next();
@@ -174,6 +174,39 @@ app.get('/health', (req, res) => {
   res.json({ status: 'ok', timestamp: new Date().toISOString() });
 });
 
+/**
+ * GET /docs/api
+ * Get complete API documentation (markdown)
+ */
+app.get('/docs/api', (req, res) => {
+  try {
+    const docPath = path.join(__dirname, '../docs/API.md');
+
+    if (!fs.existsSync(docPath)) {
+      return res.status(404).json({
+        error: 'Documentation not found',
+        message: 'API documentation file does not exist'
+      });
+    }
+
+    const docContent = fs.readFileSync(docPath, 'utf-8');
+
+    // Return as JSON with markdown content
+    res.json({
+      success: true,
+      documentation: docContent,
+      format: 'markdown',
+      lastUpdated: fs.statSync(docPath).mtime
+    });
+  } catch (error) {
+    console.error(`[API Docs] Error: ${error.message}`);
+    res.status(500).json({
+      error: 'Failed to retrieve documentation',
+      message: error.message
+    });
+  }
+});
+
 /**
  * GET /public/download/:filename
  * Public endpoint to download files without authentication
@@ -1471,6 +1504,7 @@ app.listen(PORT, () => {
   console.log(`Server running on http://localhost:${PORT}`);
   console.log('\nEndpoints:');
   console.log('  GET  /health           - Health check');
+  console.log('  GET  /docs/api         - API documentation (no auth)');
   console.log('  GET  /public/download/:filename - Public file download (no auth)');
   console.log('  GET  /info?url=        - Get video/playlist info');
   console.log('  POST /download         - Download as MP3');