install.yml verifies cargo add termlens but never cargo install termlens-cli, so a broken CLI publish is invisible until a user hits it

[vyncint]

Today — install.yml answers "does cargo add termlens work from a fresh checkout?" on Linux and macOS, in two shapes (install.yml:70). Nothing anywhere runs cargo install termlens-cli against the published crate. #310 was the cost: termlens inspect --version exited 2 in the published 0.10.0 and 0.10.1 and was found by a user of the published binary, not by CI.

Fix. A third leg (both OSes) that installs from the registry, no cache, at the version the workflow already resolves: cargo install termlens-cli --version "=$VERSION" --locked. Then the documented contract, each as an exit-code assertion:

• termlens --version and termlens inspect --version → 0, same string
• termlens inspect sh -c 'printf hi' → 0, output contains the screen and the --- exited: trailer
• termlens render --svg <a checked-in .snap> → 0, output starts with <svg
• termlens diff a.snap b.snap → 1 when they differ, 0 when the same picture
• termlens diff not-a-screen.txt a.snap → 2

Run it on the daily schedule and from release.yml's post-publish consumer step, so a bad CLI publish is red within the hour.

Done when

• The published CLI is installed and exercised on Linux and macOS in CI.
• Each exit code above is asserted, not just "the command ran".
• A deliberately broken subcommand (locally, against a path install) makes the leg fail.