Friendlier onboarding, Start Here guide, and /chat mode

[gauss-math-inc]

Summary

• port the onboarding and /chat work from math-inc/opengauss-dev#35 onto math-inc/opengauss:main
• add the mathematician-friendly Start Here guide and surface it from the README and first-stop docs
• keep improving the installer-generated guide and launcher summary without requiring Morph YAML edits
• add /chat and /start as plain-language onboarding entry points before project selection
• include the local wrapper hardening for stale runner venvs and uv-managed Python on macOS
• include the TUI command-output rendering fix so interactive command responses route through the prompt_toolkit-safe console path

Port notes

• base commit already matched opengauss/main (00fc551), so this is a straight cherry-pick port of the opengauss-dev#35 stack
• no rebase was done
• this PR is intentionally draft for soak testing before merge

Validation

• python -m pytest tests/gauss_cli/test_commands.py tests/gauss_cli/test_banner_responsive.py tests/test_cli_handoff_command.py tests/test_run_agent.py::TestBuildSystemPrompt::test_includes_open_gauss_entry_workflow_guidance tests/test_install_wrapper.py tests/test_cli_prefix_matching.py tests/test_cli_runtime_console.py -q
  • 67 passed

Follow-up / soak target

• continue checking the residual ANSI escape-fragment issue seen in some local shells; the TUI routing fix is included here, but more shell-specific reproduction may still be needed