feat(install): honour configurable install root across components

[mister2d]

• fixed kiauh.sh from launching with an error stating top_border: command not found.

• add install_root setting plus KIAUH_INSTALL_ROOT env override helper with legacy detection\n- route klipper, moonraker, extensions, and web clients to resolve paths via install root\n- create directories with sudo fallback and update backup/nginx helpers to use configured base\n- export actual backup destination in menu messaging and clarify default config.

• Fix crowsnest install root propagation and atlas dependency detection

• Ensure every crowsnest make invocation preserves the configured install root by injecting KIAUH_INSTALL_ROOT into the environment and using sudo --preserve-env, preventing installs from escaping the selected prefix. Also rerun make config/uninstall without relying on shell=True to avoid losing the environment.

• Resolve the Debian Trixie input shaper install failure by dynamically selecting between libatlas3-base and libatlas-base-dev using installed package checks and apt-cache, so users get the available ATLAS variant while the prompts and dependency installer stay in sync.

[dw-0]

Hi, thank you for your contribution.
Can you please split this PR to multiple ones, each one targeting one change at a time? This current PR seems to target 5 different situations. It is generally preferred to have scoped, incremental PRs instead of one big PR solving multiple things at once.

The first bullet point should also be already solved. I fixed that issue after receiving a bug report :)