Adds blank line separation between text and tool calls for better readability:
- Text → Tool: blank line before tool call
- Tool → Text: blank line before text
- Tool → Tool: no gap (stays tight)
Implemented via two state tracking flags in ConsoleUiWriter:
- last_output_was_text
- last_output_was_tool
Updated print_tool_output_header(), print_tool_compact(), and
print_agent_response() to check and set these flags appropriately.