Palette dynamique dans BookPlayer et admin

- BookPlayer : toutes les couleurs HSL en dur remplacées par variables CSS palette
- Admin (sidebar, formulaires, pages, book, songs, messages, media, login) : idem
- L'ambiance graphique suit maintenant la palette active partout

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

app/components/admin/AdminMediaUpload.vue

@@ -73,7 +73,7 @@ async function upload(files: FileList) {
 
 <style scoped>
 .upload-zone {
-  border: 2px dashed hsl(20 8% 22%);
+  border: 2px dashed hsl(var(--color-surface-light));
   border-radius: 0.75rem;
   padding: 2rem;
   text-align: center;
@@ -82,12 +82,12 @@ async function upload(files: FileList) {
 }
 
 .upload-zone:hover {
-  border-color: hsl(12 76% 48% / 0.4);
+  border-color: hsl(var(--color-primary) / 0.4);
 }
 
 .upload-zone--active {
-  border-color: hsl(12 76% 48%);
-  background: hsl(12 76% 48% / 0.05);
+  border-color: hsl(var(--color-primary));
+  background: hsl(var(--color-primary) / 0.05);
 }
 
 .upload-progress {
@@ -95,7 +95,7 @@ async function upload(files: FileList) {
   flex-direction: column;
   align-items: center;
   gap: 0.5rem;
-  color: hsl(20 8% 55%);
+  color: hsl(var(--color-text-muted));
   font-size: 0.85rem;
 }