refactor: Split monolithic handler into focused files

Split internal/handlers/cv.go (1,001 lines) into 5 focused files:

Structure:
- cv.go (29 lines) - CVHandler struct + constructor
- cv_pages.go (290 lines) - Page handlers (Home, CVContent, DefaultCVShortcut)
- cv_pdf.go (153 lines) - PDF export handler (ExportPDF)
- cv_htmx.go (218 lines) - HTMX toggle handlers (Length, Icons, Language, Theme)
- cv_helpers.go (385 lines) - Helper functions (skills, dates, git, templates, cookies)

Benefits:
- Single Responsibility: Each file has one clear purpose
- Improved Discoverability: Easy to find specific functionality
- Reduced Cognitive Load: 200-400 lines per file vs 1,001
- Parallel Development: No conflicts when editing different concerns
- Better Organization: Clear section markers and grouping
- Maintainability: Trade +74 lines (+7.4%) for better organization

Testing:
- All Go tests pass (fileutil, handlers, lang, cv, ui)
- Server builds and runs correctly
- All HTTP endpoints functional
- No breaking changes

Documentation:
- Create _go-learning/refactorings/003-handler-split.md
- Document architecture, benefits, and trade-offs
- Explain WHY single package vs separate packages

internal/handlers/cv_pdf.go

@@ -0,0 +1,153 @@
+package handlers
+
+import (
+	"fmt"
+	"log"
+	"net/http"
+	"strings"
+	"time"
+
+	cvmodel "github.com/juanatsap/cv-site/internal/models/cv"
+	"github.com/juanatsap/cv-site/internal/pdf"
+)
+
+// ==============================================================================
+// PDF EXPORT HANDLER
+// Handles PDF generation with customizable options (length, icons, version, theme)
+// ==============================================================================
+
+// ExportPDF handles PDF export requests using chromedp
+func (h *CVHandler) ExportPDF(w http.ResponseWriter, r *http.Request) {
+	// Extract and validate query parameters
+	lang := r.URL.Query().Get("lang")
+	if lang == "" {
+		lang = "en"
+	}
+	if lang != "en" && lang != "es" {
+		HandleError(w, r, BadRequestError("Unsupported language. Use 'en' or 'es'"))
+		return
+	}
+
+	length := r.URL.Query().Get("length")
+	if length == "" {
+		length = "short"
+	}
+	if length != "short" && length != "long" {
+		HandleError(w, r, BadRequestError("Unsupported length. Use 'short' or 'long'"))
+		return
+	}
+
+	icons := r.URL.Query().Get("icons")
+	if icons == "" {
+		icons = "show"
+	}
+	if icons != "show" && icons != "hide" {
+		HandleError(w, r, BadRequestError("Unsupported icons option. Use 'show' or 'hide'"))
+		return
+	}
+
+	version := r.URL.Query().Get("version")
+	if version == "" {
+		version = "with_skills"
+	}
+	if version != "with_skills" && version != "clean" {
+		HandleError(w, r, BadRequestError("Unsupported version. Use 'with_skills' or 'clean'"))
+		return
+	}
+
+	log.Printf("PDF export requested: lang=%s, length=%s, icons=%s, version=%s", lang, length, icons, version)
+
+	// Load CV data to get name for filename
+	cv, err := cvmodel.LoadCV(lang)
+	if err != nil {
+		HandleError(w, r, DataLoadError(err, "CV"))
+		return
+	}
+
+	// Prepare cookies to set preferences
+	cookies := map[string]string{
+		"cv-length":   length,
+		"cv-icons":    icons,
+		"cv-language": lang,
+	}
+
+	// Set theme cookie based on version parameter
+	if version == "clean" {
+		cookies["cv-theme"] = "clean"
+	} else {
+		cookies["cv-theme"] = "default"
+	}
+
+	// CRITICAL: ALWAYS force light mode for PDF generation (print-friendly)
+	// This ensures PDFs are NEVER generated in dark mode, regardless of user's preference
+	cookies["color-theme"] = "light"
+
+	// Construct URL for PDF generation (navigate to home page)
+	targetURL := fmt.Sprintf("http://%s/?lang=%s", h.serverAddr, lang)
+
+	// Determine render mode based on version parameter
+	// Clean version: use @media print CSS (print-friendly, no sidebars)
+	// Extended version: use @media screen CSS (full layout with sidebars)
+	var renderMode pdf.RenderMode
+	if version == "clean" {
+		renderMode = pdf.RenderModePrint
+	} else {
+		renderMode = pdf.RenderModeScreen
+	}
+
+	// Generate PDF with cookies and appropriate render mode
+	ctx := r.Context()
+	pdfData, err := h.pdfGenerator.GenerateFromURLWithOptions(ctx, targetURL, cookies, renderMode)
+	if err != nil {
+		log.Printf("PDF generation failed: %v", err)
+		HandleError(w, r, InternalError(err))
+		return
+	}
+
+	// Generate filename based on parameters
+	// Format: cv-{length}[-{version}]-{initials}-{year}-{lang}.pdf
+	// Note: {version} is OMITTED when it's "clean"
+	// Examples:
+	//   - cv-short-jamr-2025-es.pdf (clean version, no skills)
+	//   - cv-short-with_skills-jamr-2025-es.pdf (with skills sidebar)
+	//   - cv-long-jamr-2025-en.pdf (clean version, no skills)
+	//   - cv-long-with_skills-jamr-2025-en.pdf (with skills sidebar)
+
+	// Generate initials from name
+	nameParts := strings.Fields(cv.Personal.Name)
+	initials := ""
+	for _, part := range nameParts {
+		if len(part) > 0 {
+			// Take first letter of each name part
+			initials += string([]rune(part)[0])
+		}
+	}
+	initials = strings.ToLower(initials)
+
+	// Get current year
+	currentYear := time.Now().Year()
+
+	// Build filename: cv-{length}[-{version}]-{initials}-{year}-{lang}.pdf
+	// Omit version if it's "clean"
+	// Replace underscores with hyphens in version for filename (with_skills → with-skills)
+	var filename string
+	if version == "clean" {
+		filename = fmt.Sprintf("cv-%s-%s-%d-%s.pdf", length, initials, currentYear, lang)
+	} else {
+		versionForFilename := strings.ReplaceAll(version, "_", "-")
+		filename = fmt.Sprintf("cv-%s-%s-%s-%d-%s.pdf", length, versionForFilename, initials, currentYear, lang)
+	}
+
+	// Set response headers
+	w.Header().Set("Content-Type", "application/pdf")
+	w.Header().Set("Content-Disposition", fmt.Sprintf("attachment; filename=%s", filename))
+	w.Header().Set("Content-Length", fmt.Sprintf("%d", len(pdfData)))
+
+	// Write PDF data
+	if _, err := w.Write(pdfData); err != nil {
+		log.Printf("Error writing PDF response: %v", err)
+		return
+	}
+
+	log.Printf("PDF generated successfully: %s (%d bytes)", filename, len(pdfData))
+}