Streamline upload modal form fields and logic

- Rename "Legacy description" to "Video description"
- Group technical NIP-71 fields (Event Type, IMETA, Tracks, Segments) into a hidden "Advanced Options" section
- Automate "Summary" field to mirror "Video description" by default (with unlock toggle)
- Automate "Web seed" field to mirror "Hosted video URL"
- Automate "Content Warning" based on NSFW toggle status
- Maintain visibility of Hashtags in the main form flow
- Apply changes consistently to both Custom and Cloudflare R2 upload modes
- Fix cleanup handler registration for advanced toggle listener

js/ui/components/UploadModal.js

@@ -476,7 +476,7 @@ export class UploadModal {
   setupAdvancedToggle(toggleButton, container, icon) {
       if (!toggleButton || !container) return;
 
-      toggleButton.addEventListener('click', () => {
+      const handleToggle = () => {
          const isHidden = container.classList.contains('hidden');
          if (isHidden) {
              container.classList.remove('hidden');
@@ -489,7 +489,10 @@ export class UploadModal {
              if (toggleButton.querySelector('span')) toggleButton.querySelector('span').textContent = "Show advanced options";
              if (icon) icon.classList.remove('rotate-90');
          }
-      });
+      };
+
+      toggleButton.addEventListener('click', handleToggle);
+      this.cleanupHandlers.push(() => toggleButton.removeEventListener('click', handleToggle));
   }
 
   buildAutoGeneratedImetaVariant(file) {