feat: Add year-aware PDF shortcut URLs + Default CV modal option

## Shortcut URLs
- New routes: /cv-jamr-{year}-{lang}.pdf (e.g., /cv-jamr-2025-en.pdf)
- Year validation: Only current year accepted, returns 404 for past/future
- Auto-redirects (301) to: /export/pdf?lang={lang}&length=short&icons=show&version=with_skills
- Both languages supported: en and es

## PDF Modal Updates
- Replaced "Current View" option with "Default CV (Recommended)"
- Visual highlighting: purple gradient badge, star emoji ⭐, bold text
- Uses shortcut URL with dynamic year detection
- Clear recommendation for users (5 pages, short with skills)

## Technical Details
- Handler: DefaultCVShortcut() in internal/handlers/cv.go
- Pattern check in Home() handler for proper routing
- Helper function: window.openPdfModal() for references section
- Documentation: PDF-SHORTCUT-IMPLEMENTATION.md

Benefits:
- Memorable, shareable URLs (juan.andres.morenorub.io/cv-jamr-2025-en.pdf)
- Auto-updates yearly without code changes
- Clear user guidance for recommended CV format

static/js/main.js

@@ -541,6 +541,21 @@
     // - Focus trapping (automatic accessibility feature)
     // No JavaScript needed! All modal logic is now in HTML/CSS.
 
+    // =============================================================================
+    // PDF MODAL HELPER FUNCTION
+    // =============================================================================
+
+    /**
+     * Opens the PDF download modal
+     * Called from references section links with action="downloadPDF"
+     */
+    window.openPdfModal = function() {
+        const pdfModal = document.querySelector('#pdf-modal');
+        if (pdfModal) {
+            pdfModal.showModal();
+        }
+    };
+
     // =============================================================================
     // TOTAL REDUCTION SUMMARY
     // =============================================================================