Show exception messages for tool call errors

Claude Code sometimes only shows `Error: MCP error -32603: Internal error`
when an unexpected exception occurs during a tool call.

This change broadens the exception handling scope so the server can surface
the exception message more often, making failures easier to diagnose.

lib/mcp/server.rb

@@ -338,13 +338,11 @@ module MCP
         end
       end
 
-      begin
-        call_tool_with_args(tool, arguments)
-      rescue => e
-        report_exception(e, { request: request })
+      call_tool_with_args(tool, arguments)
+    rescue => e
+      report_exception(e, request: request)
 
-        error_tool_response("Internal error calling tool #{tool_name}: #{e.message}")
-      end
+      error_tool_response("Internal error calling tool #{tool_name}: #{e.message}")
     end
 
     def list_prompts(request)