fix: correct bash tool renderer field mapping for stdout/stderr display

## Summary - Fixes bash tool renderer in web UI to display actual command output instead of generic alerts - Changes field extraction from `stdout`/`stderr` to `stdoutPreview`/`stderrPreview` to match BashTool output structure ## Test plan - [x] Run bash command with output (e.g., `ls -la`) in web UI - [x] Verify stdout content displays in terminal-style block instead of success alert - [x] Test commands with stderr output display correctly - [x] Confirm non-zero exit codes still show output streams 🤖 Generated with [Claude Code](https://claude.ai/code)