Add ability to select multiple backlog features and edit their configuration
in bulk. Selection is limited to backlog column features in the current
branch/worktree only.
Changes:
- Add selection mode toggle in board controls
- Add checkbox selection on kanban cards (backlog only)
- Disable drag and drop during selection mode
- Hide action buttons during selection mode
- Add floating selection action bar with Edit/Clear/Select All
- Add mass edit dialog with all configuration options in single scroll view
- Add server endpoint for bulk feature updates
06c02de1cb