The unified CLI crate now matches the binary it installs. The source moved
verbatim to crates/path-cli/ via git mv (rename detection preserves history).
Extracted a `pub fn run()` library so the shim can re-export it without
duplicating source.

The old `toolpath-cli` crate name is preserved as a thin shim that depends
on path-cli and ships the same `path` binary, so `cargo install toolpath-cli`
keeps working unchanged for existing users. The shim lives outside the
workspace (`exclude = ["crates/toolpath-cli"]`) because both crates produce
a binary literally named `path`, and cargo can't write two bin targets to
the same workspace target/debug/path. Practical consequence: workspace-wide
operations (`cargo build/test --workspace`, `-p toolpath-cli`) skip the shim;
to touch it directly use `--manifest-path crates/toolpath-cli/Cargo.toml`.
The release script special-cases this in get_version and publish.

Bundled fixes:
- cmd_pathbase user-agent now reads "path-cli/<version>" instead of the
  hardcoded "toolpath-cli/<version>".
- Pre-existing rustfmt warnings in cmd_list/cmd_import/cmd_show and a
  prettier reformat in site/eleventy.config.js applied during this session.

Versioning:
- path-cli starts at 0.5.0 (continues from toolpath-cli 0.5.0).
- toolpath-cli bumps to 0.5.1 as the transitional shim release.
- Release script publishes path-cli in tier 3 and the shim in tier 4.