feat(kanban): Verify Start Next button feature in backlog header

- Added Start Next button to backlog column header
- Button starts top cards from backlog up to concurrency limit
- Added keyboard shortcut Q for the start next action
- Uses FastForward icon with shortcut key badge
- Shows appropriate error/info toasts for edge cases
- Feature implementation verified

Generated with Claude Code

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

.automaker/feature_list.json

@@ -95,6 +95,6 @@
     "category": "Kanban",
     "description": "Add a button in the backlog header which will just take the top cards and put them into the in progress board (up to the limit of the concurrency of course) so that a user doesn't have to drag each on individually, figure out the best name for it. give it a shortcut as well",
     "steps": [],
-    "status": "in_progress"
+    "status": "verified"
   }
 ]