install: auto-install yazi for tfm.nvim file manager

[Junbo-Zheng]

Summary

tfm.nvim exposes yazi as a terminal file manager (bound to <Leader>t),
but install.sh never installed yazi, so the feature silently failed on a
fresh bootstrap. Add an install_yazi step that:

• Skips if yazi is already on PATH.
• Skips (non-fatal) if cargo is absent, with a hint to install Rust.
• Installs cargo-binstall for prebuilt binaries, then yazi-fm/yazi-cli.
• Forces the musl static target on Linux x86_64/aarch64, because the
  prebuilt GNU build needs GLIBC_2.39 (absent on Ubuntu 22.04).

README's prerequisites table and the bootstrap blurb are updated to list
yazi.

Impact

• Users: New -- a fresh ./install.sh install now provides yazi so
  <Leader>t works out of the box. Existing users with yazi already on
  PATH are unaffected (skip path).
• Build: None.
• Hardware: None.
• Documentation: README prerequisites and quick-start blurb updated.
• Security & Compatibility: None -- installs a public upstream binary
  via cargo-binstall; non-fatal on any failure.

Testing

Ran ./install.sh install on Ubuntu 22.04 (x86_64, glibc 2.35):
cargo-binstall installed, yazi-fm/yazi-cli fetched the musl build,
yazi --version resolves on PATH, and <Leader>t opens yazi inside nvim.
Re-running skipped yazi (yazi already in PATH). macOS path not exercised
in this session (default target path, untested).

Signed-off-by: Junbo Zheng <3273070@qq.com>