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/AdminFieldText.vue

@@ -36,14 +36,14 @@ const id = computed(() => `field-${props.label.toLowerCase().replace(/\s+/g, '-'
 .field-label {
   font-size: 0.8rem;
   font-weight: 500;
-  color: hsl(20 8% 60%);
+  color: hsl(var(--color-text-muted));
 }
 
 .field-input {
   padding: 0.5rem 0.75rem;
   border-radius: 0.5rem;
-  border: 1px solid hsl(20 8% 18%);
-  background: hsl(20 8% 6%);
+  border: 1px solid hsl(var(--color-surface-light));
+  background: hsl(var(--color-bg));
   color: white;
   font-size: 0.875rem;
   transition: border-color 0.2s;
@@ -51,6 +51,6 @@ const id = computed(() => `field-${props.label.toLowerCase().replace(/\s+/g, '-'
 
 .field-input:focus {
   outline: none;
-  border-color: hsl(12 76% 48% / 0.5);
+  border-color: hsl(var(--color-primary) / 0.5);
 }
 </style>