fix: extract tool arguments from ToolExecutionStartEvent in sidecar

The CopilotTurnExecutionState was ignoring ToolExecutionStartData.Arguments
when creating tool-calling activity events, despite the Copilot SDK providing
them. This caused the activity panel to show 'Viewed a file' / 'Used rg'
with no contextual details (file paths, search patterns, etc.).

The fix adds NormalizeRawToolArguments to WorkflowRequestInfoInterpreter for
converting the raw object? payload (typically JsonElement) into the normalized
dictionary, then passes ToolExecutionStartData.Arguments through
CreateToolCallingActivity.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

sidecar/src/Aryx.AgentHost/Services/CopilotTurnExecutionState.cs

@@ -98,7 +98,8 @@ internal sealed class CopilotTurnExecutionState
                 string toolName = toolExecutionStart.Data.ToolName.Trim();
                 ToolNamesByCallId[toolCallId] = toolName;
                 ActiveAgent = agent;
-                AgentActivityEventDto? toolActivity = CreateToolCallingActivity(agent, toolName, toolCallId);
+                AgentActivityEventDto? toolActivity = CreateToolCallingActivity(
+                    agent, toolName, toolCallId, toolExecutionStart.Data.Arguments);
                 if (toolActivity is not null)
                 {
                     _pendingEvents.Enqueue(toolActivity);
@@ -295,7 +296,8 @@ internal sealed class CopilotTurnExecutionState
     private AgentActivityEventDto? CreateToolCallingActivity(
         AgentIdentity agent,
         string toolName,
-        string toolCallId)
+        string toolCallId,
+        object? rawArguments = null)
     {
         if (toolName.StartsWith("handoff_to_", StringComparison.Ordinal))
         {
@@ -312,6 +314,7 @@ internal sealed class CopilotTurnExecutionState
             AgentName = agent.AgentName,
             ToolName = toolName,
             ToolCallId = toolCallId,
+            ToolArguments = WorkflowRequestInfoInterpreter.NormalizeRawToolArguments(rawArguments),
         };
     }