refactor: components read the obsidian surface from its token, not a typed rgba (3108)

Thirteen rgba(20, 23, 26, ...) across six components (the task counted
eleven). They now use --v-theme-background, which Vuetify maps to obsidian;
ArtistHeader's banner fade uses --fc-chrome-rgb, since it is nav-style
chrome. A spec fails if the literal reappears outside a comment. Values are
unchanged, so nothing should render differently.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LVjrnpQjRgHdvq95rASoiR

frontend/src/components/artist/ArtistHeader.vue

@@ -103,9 +103,9 @@ const stats = computed(() => {
   padding: 0.5rem 1rem;
   background: linear-gradient(
     to bottom,
-    rgba(20, 23, 26, 0.92) 0%,
-    rgba(20, 23, 26, 0.65) 60%,
-    rgba(20, 23, 26, 0) 100%
+    rgba(var(--fc-chrome-rgb), 0.92) 0%,
+    rgba(var(--fc-chrome-rgb), 0.65) 60%,
+    rgba(var(--fc-chrome-rgb), 0) 100%
   );
   backdrop-filter: blur(2px);
   -webkit-backdrop-filter: blur(2px);

frontend/src/components/gallery/GalleryFilterBar.vue

@@ -329,7 +329,7 @@ function pushFilter(mutate) {
    opaque than the bar/nav so the controls stay legible. */
 .fc-filterbar-wrap :deep(.v-field),
 .fc-filterbar-wrap :deep(.v-btn-group) {
-  background-color: rgba(20, 23, 26, 0.72);
+  background-color: rgba(var(--v-theme-background), 0.72);
 }
 /* Media toggle (All / Images / Videos) as ONE cohesive segmented control.
    FC's global VBtn { rounded: 'pill' } default made Vuetify 4 pill-round each

frontend/src/components/modal/ImageViewer.vue

@@ -213,7 +213,7 @@ function nextFrame() {
   --fc-side-w: 320px;
   /* Obsidian haze (#14171A = 20,23,26) — same palette as TopNav,
      mid-opacity + blur so the page behind shows through faintly. */
-  background: rgba(20, 23, 26, 0.65);
+  background: rgba(var(--v-theme-background), 0.65);
   backdrop-filter: blur(8px);
   -webkit-backdrop-filter: blur(8px);
   outline: none;
@@ -221,7 +221,7 @@ function nextFrame() {
 }
 .fc-viewer__close, .fc-viewer__nav {
   position: absolute; top: 50%;
-  background: rgba(20, 23, 26, 0.7);
+  background: rgba(var(--v-theme-background), 0.7);
   color: rgb(var(--v-theme-parchment, 232 228 216));
   border: 1px solid rgb(var(--v-theme-surface-light));
   border-radius: 50%;
@@ -359,7 +359,7 @@ function nextFrame() {
     z-index: 1;
     /* Opaque obsidian so the scrolling panel never bleeds through the
        haze behind the pinned image. */
-    background: rgb(20, 23, 26);
+    background: rgb(var(--v-theme-background));
   }
   .fc-viewer__side {
     width: 100%;

frontend/src/views/ExploreView.vue

@@ -369,7 +369,7 @@ onUnmounted(() => {
 
 /* Center viewer. */
 .fc-ex__viewer {
-  background: rgb(20, 23, 26);
+  background: rgb(var(--v-theme-background));
   display: flex; flex-direction: column; min-width: 0; min-height: 0;
 }
 .fc-ex__canvas { flex: 1 1 auto; display: flex; min-height: 0; min-width: 0; }

frontend/src/views/SeriesReaderView.vue

@@ -276,7 +276,7 @@ onUnmounted(() => {
 .fc-reader__thumb img { width: 100%; height: auto; display: block; }
 .fc-reader__thumbnum {
   position: absolute; bottom: 4px; right: 4px;
-  background: rgba(20, 23, 26, 0.8); color: rgb(var(--v-theme-on-surface));
+  background: rgba(var(--v-theme-background), 0.8); color: rgb(var(--v-theme-on-surface));
   padding: 1px 5px; border-radius: 4px; font-size: 0.7rem;
 }
 .fc-reader__content {
@@ -302,7 +302,7 @@ onUnmounted(() => {
 .fc-reader__indicator {
   position: fixed; bottom: 1.5rem; right: 1.5rem;
   padding: 4px 10px; border-radius: 999px;
-  background: rgba(20, 23, 26, 0.6);
+  background: rgba(var(--v-theme-background), 0.6);
   border: 1px solid rgb(var(--v-theme-surface-light));
   font-size: 0.8rem; color: rgb(var(--v-theme-on-surface-variant));
   z-index: 100; pointer-events: none;

frontend/src/views/SeriesView.vue

@@ -338,18 +338,18 @@ onMounted(() => {
   position: absolute; top: 6px; left: 6px;
   display: inline-flex; align-items: center; gap: 2px;
   padding: 1px 6px; border-radius: 999px; font-size: 11px;
-  background: rgba(20, 23, 26, 0.75);
+  background: rgba(var(--v-theme-background), 0.75);
   color: rgb(var(--v-theme-warning, var(--v-theme-accent)));
 }
 /* Kebab sits top-right of the cover, opposite the gap badge. Tinted backing so
    it stays legible over any cover image. */
 .fc-sbcard__kebab {
   position: absolute; top: 4px; right: 4px;
-  background: rgba(20, 23, 26, 0.6) !important;
+  background: rgba(var(--v-theme-background), 0.6) !important;
   border-radius: 50%;
   color: rgb(var(--v-theme-on-surface));
 }
-.fc-sbcard__kebab:hover { background: rgba(20, 23, 26, 0.85) !important; }
+.fc-sbcard__kebab:hover { background: rgba(var(--v-theme-background), 0.85) !important; }
 .fc-sbcard__body { padding: 8px 10px; }
 .fc-sbcard__name {
   font-family: 'Fraunces', Georgia, serif; font-size: 15px; font-weight: 600;