Add comprehensive poll support with full accessibility

Features:
- Poll creation in compose dialog with up to 4 options, single/multiple choice, expiration times
- Accessible poll discovery with keyboard navigation (Enter to vote on polls in timeline)
- Poll voting dialog with radio buttons/checkboxes and proper focus management
- Poll results display using navigable list widget for accessibility
- Real-time poll validation and error handling
- Updated README with complete poll documentation

Technical improvements:
- Added poll endpoints to ActivityPub client (create_poll, vote_in_poll)
- Extended Post model with poll data fields and accessibility methods
- Enhanced timeline view with Enter key handling for poll interaction
- Simplified radio button implementation following doom launcher patterns
- Fixed undefined variable bug in poll info generation

🤖 Generated with [Claude Code](https://claude.ai/code)

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

src/main_window.py

@@ -386,7 +386,8 @@ class MainWindow(QMainWindow):
                         content=self.post_data['content'],
                         visibility=self.post_data['visibility'],
                         content_warning=self.post_data['content_warning'],
-                        in_reply_to_id=self.post_data.get('in_reply_to_id')
+                        in_reply_to_id=self.post_data.get('in_reply_to_id'),
+                        poll=self.post_data.get('poll')
                     )
                     
                     # Success