feat: enhance experience section with icons, duration, and improved styling

Experience Section Improvements:
- Increased company logo size from 48px to 64px
- Added default office building icon for companies without logos
- Increased spacing between entries (2.5rem margin, 2rem padding)
- Added visible separator lines (2px solid #ddd)
- Made dates bold (weight: 600) and larger (1.05rem)
- Changed date color to #555 for better contrast

Dynamic Duration Calculation:
- Added automatic years/months calculation for each position
- Format: "(4 years 10 months)", "(2 years)", "(6 months)"
- Smart pluralization in English and Spanish
- Handles current positions (calculates to today)
- Added Duration field to Experience model

Iconify Integration:
- Added Iconify library (v3.1.1) for icon management
- Replaced EN/ES text with round flag icons (circle-flags:us, circle-flags:es)
- Updated CV site icon to mdi:file-account
- Replaced toggle text with intuitive icons:
  * Short/Long: mdi:file-document-outline / mdi:file-document-multiple-outline
  * Logos: mdi:image-off-outline / mdi:image-multiple-outline
- Default company icon: mdi:office-building (64x64px, light gray background)

Logo Display:
- Logos now show by default (toggle checked on page load)
- Toggle controls icon visibility
- Consistent spacing with default icon placeholder

Files modified:
- internal/handlers/cv.go: Added calculateDuration() function
- internal/models/cv.go: Added Duration field to Experience struct
- templates/index.html: Iconify integration, flag icons, toggle icons
- templates/cv-content.html: Duration display, default icon logic
- static/css/main.css: Bold dates, larger font sizes
- static/css/logo-toggle.css: Icon styling, separator lines, spacing

templates/cv-content.html

@@ -74,11 +74,13 @@
 
                 {{range .CV.Experience}}
                 <div class="experience-item">
-                    {{if .CompanyLogo}}
                     <div class="company-logo">
-                        <img src="/static/images/companies/{{.CompanyLogo}}" alt="{{.Company}} logo" onerror="this.style.display='none'">
+                        {{if .CompanyLogo}}
+                        <img src="/static/images/companies/{{.CompanyLogo}}" alt="{{.Company}} logo" onerror="this.parentElement.innerHTML='<span class=\'iconify default-company-icon\' data-icon=\'mdi:office-building\' data-width=\'48\' data-height=\'48\'></span>'">
+                        {{else}}
+                        <span class="iconify default-company-icon" data-icon="mdi:office-building" data-width="48" data-height="48"></span>
+                        {{end}}
                     </div>
-                    {{end}}
                     <div class="experience-content">
                         <div class="experience-header">
                             <div class="experience-title-line">
@@ -93,6 +95,10 @@
                                     {{end}}
                                 </h4>
                                 <span class="experience-period">{{.StartDate}} / {{if .Current}}{{if eq $.Lang "es"}}presente{{else}}now{{end}}{{else}}{{.EndDate}}{{end}}</span>
+                                {{if .Duration}}
+                                <span class="experience-separator">&nbsp;-&nbsp;</span>
+                                <span class="experience-duration">{{.Duration}}</span>
+                                {{end}}
                                 <span class="experience-separator">&nbsp;-&nbsp;</span>
                                 <span class="experience-location">({{.Location}})</span>
                             </div>