Fix Share to X on mobile, update helper text

- Open window immediately before async fetch to preserve user gesture
- Update MIDI selection helper text per feedback

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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

index.html

@@ -1152,7 +1152,7 @@
 
         <div id="resultsSection" class="results-section">
             <div id="chooseHelper" class="chooser-helper" style="display:none;">
-                <p>Pick a source and generate. If it sounds off, try another.</p>
+                <p>Pick a midi source. Try another if it sounds bad, some work better than others.</p>
             </div>
 
             <div class="results-header">