Add password validation with i18n support and GitHub button improvements

- Add password field to UserUpdate schema for password change on edit
- Implement password validation in update_user endpoint
- Add i18n translations for password validation errors (ru/en)
- Update SecurityService.validate_password to support language parameter
- Add GitHub icon and repository name 'pvemanager' to header button
- Fix internal server error when updating user password
- Clean up hardcoded translations in frontend

backend/app/templates/base.html

@@ -610,6 +610,16 @@ body.update-in-progress .layout {
             </button>
             <h2>{{ page_title or title or t('nav_dashboard') }}</h2>
             <div class="header-actions">
+                <!-- GitHub Stars Button -->
+                <a href="https://github.com/markmorado/pvemanager" target="_blank" rel="noopener noreferrer" class="github-btn" title="Star us on GitHub">
+                    <i class="fa-brands fa-github"></i>
+                    <span class="github-text">pvemanager</span>
+                    <svg class="github-star-icon" xmlns="http://www.w3.org/2000/svg" width="16" height="16" viewBox="0 0 24 24" fill="currentColor">
+                        <path d="M12 .587l3.668 7.568 8.332 1.151-6.064 5.828 1.48 8.279-7.416-3.967-7.417 3.967 1.481-8.279-6.064-5.828 8.332-1.151z"/>
+                    </svg>
+                    <span class="github-stars" id="githubStars">...</span>
+                </a>
+                
                 <!-- Theme Toggle Button -->
                 <button id="themeToggle" class="theme-toggle" title="{{ t('theme') }}">
                     <svg class="icon-sun" xmlns="http://www.w3.org/2000/svg" width="20" height="20" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round">
@@ -851,6 +861,36 @@ body.update-in-progress .layout {
         }
     });
 
+    // Load GitHub stars count
+    async function loadGitHubStars() {
+        try {
+            const response = await fetch('https://api.github.com/repos/markmorado/pvemanager', {
+                headers: {
+                    'Accept': 'application/vnd.github.v3+json'
+                }
+            });
+            
+            if (response.ok) {
+                const data = await response.json();
+                const starsElement = document.getElementById('githubStars');
+                if (starsElement) {
+                    // Format number with K for thousands
+                    const stars = data.stargazers_count;
+                    const formatted = stars >= 1000 
+                        ? (stars / 1000).toFixed(1) + 'K' 
+                        : stars.toString();
+                    starsElement.textContent = formatted;
+                }
+            }
+        } catch (error) {
+            console.error('Failed to load GitHub stars:', error);
+            const starsElement = document.getElementById('githubStars');
+            if (starsElement) {
+                starsElement.textContent = '★';
+            }
+        }
+    }
+    
     // Load unread notification count
     async function loadNotificationCount() {
         try {
@@ -1268,6 +1308,9 @@ body.update-in-progress .layout {
             
             // Refresh count every 30 seconds
             setInterval(loadNotificationCount, 30000);
+            
+            // Load GitHub stars count
+            loadGitHubStars();
         }
         
         // Add click handlers for sidebar menu items to update page title