fix: References section link corruption and download filename issues

**Issue 1: URL corruption in "See this CV in..." links**
- Bug: replaceYearPlaceholder used fmt.Sprintf on ALL URLs
- URLs like "/?lang=es" were corrupted to "/?lang=es%!(EXTRA string=2025)"
- Fix: Changed to strings.ReplaceAll("{{YEAR}}", year)
- Result: Only replaces actual {{YEAR}} placeholders, leaves other URLs intact

**Issue 2: Download filename not respected**
- Bug: Shortcut URLs (cv-jamr-2025-en.pdf) redirected with HTTP 301
- Browsers used original URL filename instead of Content-Disposition header
- Fix: Generate PDF directly in DefaultCVShortcut handler
- Result: Returns PDF with correct filename in Content-Disposition header

Files changed:
- internal/models/cv.go: Fixed replaceYearPlaceholder function
- internal/handlers/cv.go: Changed redirect to direct PDF generation

Both fixes verified:
- "See this CV in Spanish" link: href="/?lang=es" ✓
- Download link: filename=cv-jamr-2025-en.pdf ✓

templates/partials/widgets/pdf-toast.html

@@ -0,0 +1,14 @@
+{{define "pdf-toast"}}
+<!-- PDF Download Toast Notification -->
+<div id="pdf-toast" class="success-toast no-print" role="status" aria-live="polite" aria-atomic="true">
+    <span class="toast-icon" id="pdf-toast-icon">📥</span>
+    <div class="toast-content">
+        <p class="toast-title" id="pdf-toast-title">{{if eq .Lang "es"}}Preparando PDF{{else}}Preparing PDF{{end}}</p>
+        <p class="toast-message" id="pdf-toast-message"></p>
+    </div>
+    <button aria-label="{{if eq .Lang "es"}}Cerrar notificación{{else}}Close notification{{end}}" class="toast-close" onclick="document.getElementById('pdf-toast').classList.remove('show')">×</button>
+    <div class="toast-progress">
+        <div class="toast-progress-bar" id="pdf-toast-progress"></div>
+    </div>
+</div>
+{{end}}