BugTraceAI CLI 4.0.19-beta — installer fixes

The installer now prepares missing Docker Engine and Compose on Linux instead
of stopping with a manual-install message. Working runtimes are reused, and
the global btai command uses the same Docker access as the installer.

• Choose TUI, API/MCP or both, then local Python or Docker. TUI-only Docker
  installations do not start server services or publish ports.
• Fresh Ubuntu installs verify a complete virtual environment with pip and
  prepare missing system dependencies. Local Linux installs select PyTorch CPU.
• Docker builds select the correct Nuclei binary for AMD64 or ARM64.
• Installation profiles are saved after successful installation, and --reuse
  keeps the selected profile and configured ports.

Validation included 44 CLI installer tests, real installation of all three
Docker profiles, a complete local installation on Ubuntu 24.04, API/MCP
responses, global btai, Chromium startup and TUI tabs/Provider/Auth controls.
Native macOS and Apple Silicon installation were not tested on physical hardware.

For an existing checkout, update the repository and repair the saved profile:

git pull --ff-only
./install.sh --reuse

If the previous installer stopped before saving a profile, run ./install.sh
instead of --reuse to choose the interfaces and runtime again.

For fresh installations, follow INSTALLATION.md.