Refine planner mode UI and error handling

Improve planner mode user experience with better error reporting,
cleaner tool output, and consistent log file placement.

- Propagate and display classified LLM errors to users with
  appropriate icons and context
- Display tool calls on single lines with truncated arguments
- Show LLM text responses without overwriting via UiWriter
- Ensure all logs write to workspace/logs directory consistently
- Set G3_WORKSPACE_PATH early in planning mode initialization

crates/g3-cli/src/machine_ui_writer.rs

@@ -40,7 +40,7 @@ impl UiWriter for MachineUiWriter {
         println!("CONTEXT_THINNING: {}", message);
     }
 
-    fn print_tool_header(&self, tool_name: &str) {
+    fn print_tool_header(&self, tool_name: &str, _tool_args: Option<&serde_json::Value>) {
         println!("TOOL_CALL: {}", tool_name);
     }