fix(services/spotlight): improve MPRIS artwork handling and scope keyword searches to single plugin

- mpris: native MediaArt cache lookup, dedupe play/pause emission, safe
  cleanup, artwork polling for already-playing browser players, drop
  os.system seek fallback
- spotlight: scope plugin keyword and detect() matches to a single plugin
  via search_single instead of global search; register clipboard keywords
  (clip/clipboard)

src/styles/window/spotlight.css

@@ -1,21 +1,3 @@
-@keyframes app-slot-shine {
-    from {
-        background-color: @fg-a12;
-    }
-    to {
-        background-color: alpha(@surface-bright, 0.5);
-    }
-}
-
-@keyframes header-shine {
-    from {
-        background-color: @fg-a12;
-    }
-    to {
-        background-color: alpha(@surface-bright, 0.3);
-    }
-}
-
 #spotlight {
     margin: 8px;
     padding: 5px;
@@ -40,10 +22,6 @@
     transition: background-color apply(transition-medium) ease-in-out;
 }
 
-.app-search-header.shine {
-    animation: header-shine 1s ease-in-out infinite alternate;
-}
-
 .app-slot {
     padding: 8px;
     border: solid 1px transparent;
@@ -64,10 +42,6 @@
     background-color: @primary-a20;
 }
 
-.app-slot.shine {
-    animation: app-slot-shine 0.3s ease-in-out;
-}
-
 .app-title {
     color: @foreground;
     font-size: apply(font-base);