fix(api): Remove non-existent description field from workers endpoint

The Worker model has no 'description' field. This was causing 500 errors
on the /api/workers endpoint. Replaced with 'agent_type' and 'capabilities'
which are actual fields.

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

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

Author: mjunaidca

apps/api/src/taskflow_api/routers/workers.py

@@ -180,7 +180,8 @@ async def list_workers(
             "handle": w.handle,
             "name": w.name,
             "type": w.type,
-            "description": w.description,
+            "agent_type": w.agent_type,
+            "capabilities": w.capabilities,
         }
         for w in result.all()
     ]