Add concurrency slider for automode to control max parallel agents

- Added maxConcurrency state to app-store with persistence
- Created slider UI component using Radix UI
- Added concurrency slider to board-view header (left of Auto Mode button)
- Updated use-auto-mode hook to expose canStartNewTask based on limit
- Block dragging features to in_progress when at max concurrency
- Added test utilities for concurrency slider interactions

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

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

.automaker/feature_list.json

@@ -34,13 +34,13 @@
       "3. wait until it is moved to verified",
       "4. assert modal is hidden"
     ],
-    "status": "backlog"
+    "status": "in_progress"
   },
   {
     "id": "feature-1765254432072-bqk25kivv",
     "category": "Automode",
     "description": "Add a concurrency slider left of automode so I can specify how many max agents should be running at one time.  if we are at max, do not pull over more tasks from the backlog",
     "steps": [],
-    "status": "backlog"
+    "status": "verified"
   }
 ]