Upload progress spinner + duplicate game detection

Two features:

1. Progress indicator: when upload starts, the dialog switches from
   IGDB results to a centered spinner with 'Uploading and processing'
   text + filename. The Cancel button stays visible but disabled.

2. Duplicate game blocking: before upload, checks if a game with the
   same title (case-insensitive) already exists in the library.
   Frontend checks against the loaded games list; backend also
   checks as a second line of defense. Shows ⚠️ message in dialog.
   Existing unique-ID suffix logic (foo-2, foo-3) is still in place
   but now only reached when titles actually differ.

frontend/src/pages/Library.svelte

@@ -16,6 +16,7 @@
   let searchError = $state("");
   let igdbResults = $state(null); // null=loading, []=no results, [{...}]=matches
   let manualSearched = $state(false); // true after user clicked Search manually
+  let duplicateError = $state(""); // title of duplicate game if blocked
 
   let fileInput;
 
@@ -80,12 +81,25 @@
     igdbResults = null;
     searchError = "";
     manualSearched = false;
+    duplicateError = "";
   }
 
   async function doUpload(title, igdbId) {
     if (!pendingFile) return;
+
+    // Block duplicates: case-insensitive title match
+    const finalTitle = title || pendingFileName;
+    if (finalTitle) {
+      const dup = games.find(g => g.title?.toLowerCase() === finalTitle.toLowerCase());
+      if (dup) {
+        duplicateError = `"${dup.title}" is already in your library`;
+        return;
+      }
+    }
+
     uploading = true;
     uploadError = "";
+    duplicateError = "";
     try {
       await uploadGame(pendingFile, title || undefined, igdbId);
       cancelUpload();
@@ -134,7 +148,18 @@
         <p class="upload-file-name">{pendingFileName}.zip</p>
 
         <div class="upload-dialog-body">
-          {#if searching}
+          {#if uploading}
+            <div class="upload-progress">
+              <div class="upload-progress-spinner"></div>
+              <p class="upload-progress-text">Uploading and processing</p>
+              <p class="upload-progress-sub">{pendingFileName}.zip</p>
+              <p class="upload-progress-note">This may take a while for large games</p>
+            </div>
+          {:else if duplicateError}
+            <div class="status-msg error-msg">
+              ⚠️ {duplicateError}
+            </div>
+          {:else if searching}
             <div class="status-msg">Searching IGDB for "{pendingFileName}"...</div>
           {:else if igdbResults !== null && igdbResults.length > 0}
             <p class="match-label">Select a match or enter a custom title:</p>
@@ -490,4 +515,40 @@
     background: #332211;
     border-color: #ffaa44;
   }
+
+  /* ─── Upload Progress ──────────────────────────── */
+  .upload-progress {
+    display: flex;
+    flex-direction: column;
+    align-items: center;
+    padding: 40px 20px;
+    text-align: center;
+  }
+  .upload-progress-spinner {
+    width: 40px;
+    height: 40px;
+    border: 3px solid var(--border);
+    border-top: 3px solid var(--phosphor);
+    border-radius: 50%;
+    animation: spin 0.8s linear infinite;
+    margin-bottom: 16px;
+  }
+  @keyframes spin {
+    to { transform: rotate(360deg); }
+  }
+  .upload-progress-text {
+    color: var(--text);
+    font-size: 1rem;
+    margin-bottom: 4px;
+  }
+  .upload-progress-sub {
+    color: var(--text-dim);
+    font-size: 0.85rem;
+  }
+  .upload-progress-note {
+    color: var(--text-dim);
+    font-size: 0.75rem;
+    margin-top: 8px;
+    opacity: 0.7;
+  }
 </style>

src/main/java/com/dostalgia/UploadResource.java

@@ -48,6 +48,15 @@ public class UploadResource {
 
         String gameId = GameService.sanitizeId(title);
 
+        // Check for duplicate by title (case-insensitive)
+        for (var g : svc.list()) {
+            if (g.getTitle() != null && g.getTitle().equalsIgnoreCase(title)) {
+                return Response.status(409)
+                    .entity(Map.of("error", "\"" + title + "\" is already in your library"))
+                    .build();
+            }
+        }
+
         // Ensure unique ID
         String baseId = gameId;
         int counter = 2;