fix(post): preserve content when signing or publishing

Critical fix: Don't clear editor content until publish succeeds.

**The Problem:**
- RichEditor automatically cleared content on submit
- Content was wiped immediately when clicking "Publish"
- User lost their content before knowing if publish succeeded

**The Solution:**
- Remove automatic `clearContent()` from RichEditor's handleSubmit
- Let PostViewer control when to clear the editor
- Only clear editor after successful publish (successCount > 0)

**User Experience Now:**
- Click "Publish" → content stays visible while publishing
- Publishing succeeds → content clears, show preview
- Publishing fails → content stays, user can edit and retry
- User rejects signing → content stays, can try again

No more losing your post to a rejected signature or failed publish!

src/components/PostViewer.tsx

@@ -503,6 +503,9 @@ export function PostViewer({ windowId }: PostViewerProps = {}) {
             localStorage.removeItem(draftKey);
           }
 
+          // Clear editor content
+          editorRef.current?.clear();
+
           // Show published preview
           setShowPublishedPreview(true);
 

src/components/editor/RichEditor.tsx

@@ -402,7 +402,7 @@ export const RichEditor = forwardRef<RichEditorHandle, RichEditorProps>(
             serialized.eventRefs,
             serialized.addressRefs,
           );
-          editorInstance.commands.clearContent();
+          // Don't clear content here - let the parent component decide when to clear
         }
       },
       [onSubmit],