fix: Add headless Chrome configuration for CI environment

- Configure chromedp with headless mode and CI-friendly flags
- Add --no-sandbox flag (required for Docker/CI environments)
- Add --disable-gpu and --disable-dev-shm-usage for stability
- Use NewExecAllocator with DefaultExecAllocatorOptions

This fixes 'chrome failed to start' errors in GitHub Actions CI where
Chrome needs to run without a display and with relaxed sandbox restrictions.

internal/pdf/generator.go

@@ -32,10 +32,25 @@ func (g *Generator) GenerateFromURL(ctx context.Context, url string) ([]byte, er
 	ctx, cancel := context.WithTimeout(ctx, g.timeout)
 	defer cancel()
 
-	// Create chromedp context
-	allocCtx, allocCancel := chromedp.NewContext(ctx)
+	// Create chromedp options for headless mode (especially for CI environments)
+	opts := append(chromedp.DefaultExecAllocatorOptions[:],
+		chromedp.Flag("headless", true),
+		chromedp.Flag("disable-gpu", true),
+		chromedp.Flag("no-sandbox", true),
+		chromedp.Flag("disable-dev-shm-usage", true),
+	)
+
+	// Create exec allocator with custom options
+	allocCtx, allocCancel := chromedp.NewExecAllocator(ctx, opts...)
 	defer allocCancel()
 
+	// Create chromedp context
+	browserCtx, browserCancel := chromedp.NewContext(allocCtx)
+	defer browserCancel()
+
+	// Use browserCtx instead of allocCtx for chromedp operations
+	allocCtx = browserCtx
+
 	// Buffer to store PDF
 	var pdfBuffer []byte