UI: Standardize buttons and design system across the application

- Created a unified button system in style.css with primary, secondary, and icon variants.
- Standardized cards, inputs, and layout components for a more premium look.
- Refactored header, login, anime/series cards, and watchlist/downloads sections to use the new design system.
- Cleaned up inline styles and redundant local style blocks in templates.
- Updated JS-generated buttons to follow the new global styling.

static/js/recommendations.js

@@ -26,7 +26,7 @@ async function loadRecommendations() {
                     <p style="font-size: 12px; margin-top: 10px; color: #888;">
                         Soit l'API MyAnimeList est inaccessible, soit vous n'avez pas encore de téléchargements.
                     </p>
-                    <button class="btn-secondary btn-small" onclick="loadRecommendations()" style="margin-top: 10px;">
+                    <button class="btn btn-secondary btn-small" onclick="loadRecommendations()" style="margin-top: 10px;">
                         🔄 Réessayer
                     </button>
                 </div>
@@ -40,7 +40,7 @@ async function loadRecommendations() {
             <div class="no-results">
                 <p>❌ Erreur lors du chargement des recommandations.</p>
                 <p style="font-size: 12px; margin-top: 10px; color: #ff6b6b;">${error.message}</p>
-                <button class="btn-secondary btn-small" onclick="loadRecommendations()" style="margin-top: 10px;">
+                <button class="btn btn-secondary btn-small" onclick="loadRecommendations()" style="margin-top: 10px;">
                     🔄 Réessayer
                 </button>
             </div>
@@ -75,7 +75,7 @@ async function loadLatestReleases() {
                     <p style="font-size: 12px; margin-top: 10px; color: #888;">
                         L'API MyAnimeList pourrait être temporairement inaccessible.
                     </p>
-                    <button class="btn-secondary btn-small" onclick="loadLatestReleases()" style="margin-top: 10px;">
+                    <button class="btn btn-secondary btn-small" onclick="loadLatestReleases()" style="margin-top: 10px;">
                         🔄 Réessayer
                     </button>
                 </div>
@@ -89,7 +89,7 @@ async function loadLatestReleases() {
             <div class="no-results">
                 <p>❌ Erreur lors du chargement des sorties.</p>
                 <p style="font-size: 12px; margin-top: 10px; color: #ff6b6b;">${error.message}</p>
-                <button class="btn-secondary btn-small" onclick="loadLatestReleases()" style="margin-top: 10px;">
+                <button class="btn btn-secondary btn-small" onclick="loadLatestReleases()" style="margin-top: 10px;">
                     🔄 Réessayer
                 </button>
             </div>
@@ -180,10 +180,10 @@ function renderRecommendationCard(anime) {
             ` : ''}
 
             <div class="anime-card-actions">
-                <button class="btn-secondary btn-small" onclick="window.open('${escapeHtml(anime.url)}', '_blank')">
+                <button class="btn btn-secondary btn-small" onclick="window.open('${escapeHtml(anime.url)}', '_blank')">
                     🔗 MAL
                 </button>
-                <button class="btn-primary btn-small" onclick="searchAnimeOnProviders('${escapeHtml(anime.title)}')">
+                <button class="btn btn-primary btn-small" onclick="searchAnimeOnProviders('${escapeHtml(anime.title)}')">
                     📥 Télécharger
                 </button>
             </div>
@@ -233,10 +233,10 @@ function renderReleaseCard(anime) {
             ` : ''}
 
             <div class="anime-card-actions">
-                <button class="btn-secondary btn-small" onclick="window.open('${escapeHtml(anime.url)}', '_blank')">
+                <button class="btn btn-secondary btn-small" onclick="window.open('${escapeHtml(anime.url)}', '_blank')">
                     🔗 MAL
                 </button>
-                <button class="btn-primary btn-small" onclick="searchAnimeOnProviders('${escapeHtml(anime.title)}')">
+                <button class="btn btn-primary btn-small" onclick="searchAnimeOnProviders('${escapeHtml(anime.title)}')">
                     📥 Télécharger
                 </button>
             </div>