feat: redesign download UX — batch select, season download, toast feedback

Episode list:
- Added 'Saison complète' header button to download all episodes at once
- Added multi-select mode with checkboxes for batch episode download
- Individual download buttons now show visual feedback (checkmark + reset)
- Better grid/list toggle with selection state indicators

Search results (anime + series):
- Redesigned download dropdown with icons, descriptions, spinner on click
- Smooth scale/opacity transitions on dropdown open/close
- Consistent btn-success color for all download actions

Series search JS:
- Replaced basic <select> with scrollable episode list inline
- Added 'Tout télécharger' button per series card
- Replaced all alert() calls with toast notifications
- Episode buttons show checkmark on successful download

Anime details JS:
- Added batch download button next to episode select
- Fixed pre-existing lint error (escaped quote in translateSynopsis)
- Standardized download icon to fa-arrow-down across all cards

Recommendations + Tabs JS:
- Unified download button color (btn-success) across all card types
- Consistent icon (fa-arrow-down) for download actions

Toast system:
- Connected to existing Alpine.js toast infrastructure (show-toast events)

static/js/recommendations.js

@@ -190,8 +190,8 @@ function renderRecommendationCard(anime) {
                     <button class="btn btn-secondary btn-sm" onclick="window.open('${escapeHtml(anime.url)}', '_blank')">
                         <i class="fa-solid fa-link"></i> MAL
                     </button>
-                    <button class="btn btn-primary btn-sm" onclick="searchAnimeOnProviders('${escapeHtml(anime.title)}')">
-                        <i class="fa-solid fa-download"></i> Télécharger
+                    <button class="btn btn-success btn-sm" onclick="searchAnimeOnProviders('${escapeHtml(anime.title)}')">
+                        <i class="fa-solid fa-arrow-down"></i> Télécharger
                     </button>
                 </div>
             </div>
@@ -247,8 +247,8 @@ function renderReleaseCard(anime) {
                     <button class="btn btn-secondary btn-sm" onclick="window.open('${escapeHtml(anime.url)}', '_blank')">
                         <i class="fa-solid fa-link"></i> MAL
                     </button>
-                    <button class="btn btn-primary btn-sm" onclick="searchAnimeOnProviders('${escapeHtml(anime.title)}')">
-                        <i class="fa-solid fa-download"></i> Télécharger
+                    <button class="btn btn-success btn-sm" onclick="searchAnimeOnProviders('${escapeHtml(anime.title)}')">
+                        <i class="fa-solid fa-arrow-down"></i> Télécharger
                     </button>
                 </div>
             </div>