feat: pre-populate upload title with filename when no IGDB matches

When a game ZIP is selected and IGDB returns no matches, the search
box is now pre-filled with the filename (minus .zip extension) so
the user can edit it rather than typing from scratch.

frontend/src/pages/Library.svelte

@@ -130,7 +130,7 @@
     const name = file.name.replace(/\.zip$/i, "");
     pendingFile = file;
     pendingFileName = name;
-    pendingTitle = "";
+    pendingTitle = name;
     igdbResults = null;
     searching = true;
     searchError = "";
@@ -369,12 +369,12 @@
                   {/if}
                 </div>
               {:else}
-                <p class="match-label">No matches found. Enter a title to search IGDB:</p>
+                <p class="match-label">No matches found. Edit the title below and search IGDB:</p>
               {/if}
               <div class="upload-custom-row">
                 <input
                   type="text"
-                  placeholder="Search IGDB..."
+                  placeholder="Edit title..."
                   bind:value={pendingTitle}
                   disabled={uploading || searching}
                   onkeydown={(e) => e.key === "Enter" && handleManualSearch()}