Add cheznav info subcommand

[djetelina]

Adds a non-interactive cheznav info subcommand that prints diagnostics and exits without launching the TUI:

cheznav 0.3.0
chezmoi: chezmoi version v2.70.5, built at 2026-06-04T09:10:45Z (/usr/bin/chezmoi)
config:  /home/you/.config/chezmoi/chezmoi.toml
source:  /home/you/.local/share/chezmoi (git repo)

It reports:

• cheznav's own version
• whether chezmoi is installed and its version (or a clear "not found" message)
• the detected chezmoi config file, or where it looked if none exists (honors --chezmoi-config)
• whether a chezmoi source directory is initialized (and whether it's a git repo)

Why

Quick environment diagnostics, and a non-TUI entry point for packaging smoke tests. The Homebrew formula needs a test that exercises real functionality — the cookbook rejects bare --help/--version checks — and cheznav otherwise only launches the TUI. cheznav info gives brew test a deterministic, meaningful command to assert against.

Implementation

• New cheznav/info.py holds print_info; main.py only wires up the info subparser.
• No new dependencies; runs synchronously and never imports the TUI path.
• tests/test_cli_info.py covers installed/missing chezmoi, config found/absent, and initialized/uninitialized source. Full suite: 92 passed.
• README usage updated.