feat: enhance PDF export with 4 customizable parameters

Add comprehensive parameter support to /export/pdf endpoint:
- lang: Language selection (en/es)
- length: CV length (short/long)
- icons: Icon visibility (show/hide)
- version: Theme variant (extended/clean)

Backend Changes:
- Enhanced PDF generator with cookie injection for user preferences
- Cookies set before chromedp navigation to apply all preferences
- Updated filename pattern: CV-{Name}-{lang}-{length}-{version}.pdf
- Comprehensive parameter validation with descriptive error messages
- All parameters optional with sensible defaults (en, short, show, extended)

Testing:
- Added pdf_test.go with parameter validation tests
- Tests cover all valid/invalid parameter combinations
- Tests verify default parameter application

Documentation:
- Updated API documentation (doc/3-API.md)
- Added detailed parameter descriptions and examples
- Updated quick reference with all parameter options
- Added process flow diagram showing cookie injection
- Documented error responses for each invalid parameter

Implementation Details:
- Cookie domain set to "localhost" for chromedp context
- Cookies: cv-language, cv-length, cv-icons, cv-theme
- PDF generation leverages existing @media print CSS
- No changes to frontend CSS or templates

Tested:
- Parameter validation (✅ All invalid params rejected correctly)
- Default parameters (✅ Applied when params omitted)
- PDF generation with all parameter combinations (✅ Working)

internal/pdf/generator.go

@@ -6,6 +6,7 @@ import (
 	"io"
 	"time"
 
+	"github.com/chromedp/cdproto/network"
 	"github.com/chromedp/cdproto/page"
 	"github.com/chromedp/chromedp"
 )
@@ -77,6 +78,83 @@ func (g *Generator) GenerateFromURL(ctx context.Context, url string) ([]byte, er
 	return pdfBuffer, nil
 }
 
+// GenerateFromURLWithCookies generates a PDF from a given URL with custom cookies
+func (g *Generator) GenerateFromURLWithCookies(ctx context.Context, url string, cookies map[string]string) ([]byte, error) {
+	// Create context with timeout
+	ctx, cancel := context.WithTimeout(ctx, g.timeout)
+	defer cancel()
+
+	// Create chromedp context
+	allocCtx, allocCancel := chromedp.NewContext(ctx)
+	defer allocCancel()
+
+	// Buffer to store PDF
+	var pdfBuffer []byte
+
+	// Build tasks - set cookies BEFORE navigation
+	var tasks chromedp.Tasks
+
+	// Add cookies if provided - must be done before navigation
+	if len(cookies) > 0 {
+		tasks = append(tasks, chromedp.ActionFunc(func(ctx context.Context) error {
+			// Set cookies with domain (extract from URL)
+			// For localhost:1999, domain should be "localhost"
+			domain := "localhost"
+
+			for name, value := range cookies {
+				expr := network.SetCookie(name, value).
+					WithDomain(domain).
+					WithPath("/").
+					WithHTTPOnly(true).
+					WithSecure(false). // Set to true in production with HTTPS
+					WithSameSite(network.CookieSameSiteStrict)
+
+				if err := expr.Do(ctx); err != nil {
+					return fmt.Errorf("failed to set cookie %s: %w", name, err)
+				}
+			}
+			return nil
+		}))
+	}
+
+	// Navigate to URL
+	tasks = append(tasks, chromedp.Navigate(url))
+
+	// Wait for page to be ready
+	tasks = append(tasks,
+		chromedp.WaitReady("body"),
+		// Small delay to ensure all content is loaded
+		chromedp.Sleep(500*time.Millisecond),
+		// Generate PDF with print-optimized settings
+		chromedp.ActionFunc(func(ctx context.Context) error {
+			var err error
+			pdfBuffer, _, err = page.PrintToPDF().
+				WithPrintBackground(true).
+				WithPreferCSSPageSize(true).
+				WithMarginTop(0).
+				WithMarginBottom(0).
+				WithMarginLeft(0).
+				WithMarginRight(0).
+				WithPaperWidth(8.27).  // A4 width in inches
+				WithPaperHeight(11.69). // A4 height in inches
+				Do(ctx)
+			return err
+		}),
+	)
+
+	// Run chromedp tasks
+	err := chromedp.Run(allocCtx, tasks)
+	if err != nil {
+		return nil, fmt.Errorf("chromedp execution failed: %w", err)
+	}
+
+	if len(pdfBuffer) == 0 {
+		return nil, fmt.Errorf("generated PDF is empty")
+	}
+
+	return pdfBuffer, nil
+}
+
 // StreamFromURL generates a PDF and writes it to the provided writer
 func (g *Generator) StreamFromURL(ctx context.Context, url string, w io.Writer) error {
 	pdfData, err := g.GenerateFromURL(ctx, url)