style: change instance ID format from ': 1' to '#1'

- Cleaner display format for parallel agent instances
- Shows as 'PM-1-DayStatusSummarizer#1' and 'PM-1-DayStatusSummarizer#2'
- Appears in both progress panel and chat headers

Author: Valeriy_Pavlovich

src/fast_agent/agents/workflow/agents_as_tools_agent.py

@@ -320,7 +320,7 @@ async def run_tools(self, request: PromptMessageExtended) -> PromptMessageExtend
                 child = self._child_agents.get(tool_name) or self._child_agents.get(self._make_tool_name(tool_name))
                 if child and hasattr(child, '_name'):
                     original_names[cid] = child._name
-                    child._name = f"{child._name}: {i}"
+                    child._name = f"{child._name}#{i}"
 
         # Now create tasks with modified names
         for cid in id_list: