Add tag cloud feature with k-means clustering and CUDA support

Introduces an Explore view with a tag cloud that clusters image embeddings
using cosine k-means and labels clusters via vocabulary-nearest-neighbour
CLIP matching. Vocabulary embeddings are disk-cached (FNV hash-keyed) to
avoid redundant inference. Enables CUDA for candle dependencies and adds a
build.rs check that surfaces a clear error when the toolkit is missing.

src/App.tsx

@@ -5,12 +5,14 @@ import { BackgroundTasks } from "./components/BackgroundTasks";
 import { Toolbar } from "./components/Toolbar";
 import { Gallery } from "./components/Gallery";
 import { Lightbox } from "./components/Lightbox";
+import { TagCloud } from "./components/TagCloud";
 
 export default function App() {
   const loadFolders = useGalleryStore((state) => state.loadFolders);
   const loadBackgroundJobProgress = useGalleryStore((state) => state.loadBackgroundJobProgress);
   const loadImages = useGalleryStore((state) => state.loadImages);
   const subscribeToProgress = useGalleryStore((state) => state.subscribeToProgress);
+  const activeView = useGalleryStore((state) => state.activeView);
 
   useEffect(() => {
     loadFolders().then(() => {
@@ -30,9 +32,18 @@ export default function App() {
     <div className="flex h-screen bg-gray-950 text-white overflow-hidden select-none">
       <Sidebar />
       <main className="flex-1 flex flex-col min-w-0">
-        <Toolbar />
-        <BackgroundTasks />
-        <Gallery />
+        {activeView === "explore" ? (
+          <>
+            <BackgroundTasks />
+            <TagCloud />
+          </>
+        ) : (
+          <>
+            <Toolbar />
+            <BackgroundTasks />
+            <Gallery />
+          </>
+        )}
       </main>
       <Lightbox />
     </div>