fix: show loading screen during extension upload search

Previously when loading an upload from extension that hadn't been searched yet,
the app would immediately navigate to the results page showing 'none' for all
matches, then update them as the search progressed.

Now it behaves like the file upload flow:
- Shows loading screen during search
- Navigates to results only after search completes and results are saved
- If upload already has matches, navigates to results immediately

packages/web/src/App.tsx

···
         }));
 
         setSearchResults(loadedResults);
-        setCurrentStep("results");
 
-        // If no matches yet, trigger search
+        // If no matches yet, trigger search BEFORE navigating to results
         if (!hasMatches) {
           const followLexicon = ATPROTO_APPS[currentDestinationAppId]?.followLexicon;
 
···
             loadedResults,
             (message) => setStatusMessage(message),
             async (finalResults) => {
-              // Search complete - save results
-              // finalResults contains the updated results with all matches found
+              // Search complete - save results and navigate to results page
               await saveResults(uploadId, platform, finalResults);
+              setCurrentStep("results");
             },
             followLexicon
           );
+        } else {
+          // Already has matches, navigate to results immediately
+          setCurrentStep("results");
         }
 
         // Announce to screen readers only - visual feedback is navigation to results page