Resolve two critical issues in planner mode that persisted through
multiple fix attempts:
1. Remove excessive whitespace between tool call displays by replacing
direct println!() calls with ui_writer methods and eliminating
redundant newlines in agent response streaming.
2. Ensure all log files (errors, sessions, tool calls, context dumps)
are written to <workspace>/logs instead of codepath by properly
initializing G3_WORKSPACE_PATH from --workspace argument.
87bceba54f