Store language preference in localStorage for clean URL persistence

Changes:
- Save selected language to localStorage when user switches languages
- On page load with clean URL: check localStorage and load saved language preference
- If no localStorage preference exists, default to server's language choice
- Update language button active states based on localStorage preference
- Keep URLs clean (no lang parameter added) while maintaining language choice
- If URL has lang parameter, save it to localStorage for consistency

How it works:
1. Visit / (clean) → Shows English (default)
2. Switch to Spanish → Saves 'es' to localStorage, loads Spanish content
3. Click logo (clean URL /) → Page loads, checks localStorage, loads Spanish
4. Language persists across clean URL navigations via localStorage

This solves: Clean URLs + Language persistence

templates/index.html

@@ -385,6 +385,9 @@
             });
             event.target.closest('.selector-btn').classList.add('active');
 
+            // Save language preference to localStorage
+            localStorage.setItem('cv-language', lang);
+
             // Use HTMX to load new content
             htmx.ajax('GET', `/cv?lang=${lang}`, {
                 target: '#cv-content',
@@ -397,15 +400,8 @@
             if (urlHadLangParam) {
                 url.searchParams.set('lang', lang);
                 window.history.pushState({}, '', url);
-
-                // Update logo and title links to include current language
-                document.getElementById('logoLink').href = `/?lang=${lang}`;
-                document.getElementById('titleLink').href = `/?lang=${lang}`;
-            } else {
-                // Keep URL clean, but update logo/title links to stay clean too
-                document.getElementById('logoLink').href = '/';
-                document.getElementById('titleLink').href = '/';
             }
+            // If URL is clean, keep it clean (don't add lang parameter)
 
             // Update html lang attribute
             document.documentElement.lang = lang;
@@ -493,11 +489,30 @@
         document.addEventListener('DOMContentLoaded', function() {
             const paper = document.querySelector('.cv-paper');
 
-            // Initialize logo/title links based on whether URL has lang parameter
-            if (urlHadLangParam) {
-                const currentLang = new URLSearchParams(window.location.search).get('lang') || 'en';
-                document.getElementById('logoLink').href = `/?lang=${currentLang}`;
-                document.getElementById('titleLink').href = `/?lang=${currentLang}`;
+            // Handle language preference
+            const urlLang = new URLSearchParams(window.location.search).get('lang');
+            const savedLang = localStorage.getItem('cv-language');
+
+            if (!urlLang && savedLang) {
+                // URL is clean but we have a saved preference - load that language
+                htmx.ajax('GET', `/cv?lang=${savedLang}`, {
+                    target: '#cv-content',
+                    swap: 'innerHTML swap:0ms settle:0ms'
+                });
+
+                // Update button states
+                document.querySelectorAll('.language-selector .selector-btn').forEach(btn => {
+                    btn.classList.remove('active');
+                    if (btn.getAttribute('onclick').includes(savedLang)) {
+                        btn.classList.add('active');
+                    }
+                });
+
+                // Update html lang attribute
+                document.documentElement.lang = savedLang;
+            } else if (urlLang) {
+                // Save URL language to localStorage
+                localStorage.setItem('cv-language', urlLang);
             }
 
             // Restore CV length preference