ci: termlens-cli is on crates.io; make the next release say so honestly

[vyncint]

termlens-cli 0.10.0 is published (2026-09-08, via the publish-cli.yml bootstrap). Verified the way a user meets it, not from this tree:

$ cargo install termlens-cli --locked        # Downloaded termlens-cli v0.10.0
$ termlens --version                         # termlens 0.10.0
$ termlens inspect --size 30x4 sh -c 'printf "hello from a pty"'
size: 30x4  cursor: 0,16
hello from a pty
--- exited: exit code 0 ---
$ termlens diff --color never before.snap after.snap.new ; echo $?
… 2 rows unchanged
styles: 0: 0-4 fg=6 bold; 7-13 reverse → 0-4 fg=6 bold
1

The reason this is a PR and not just a report. release.yml's CLI step guarded itself with "does crates.io know this crate?" and skipped with a warning. crates.io now answers 200, so next tag it will run — and Trusted Publishing is configured per crate, so the OIDC token minted for termlens does not carry termlens-cli until that crate has a publisher of its own. The failure would be a bare 403, arriving after termlens is already published. The step now names the likely cause, the exact place to fix it, and warns that re-running the job fails on the other crate instead.

docs/RELEASING.md claimed publishing stores no secret anywhere; that is currently false, so the prerequisites now list both crates, mark termlens-cli as not yet linked, and carry the teardown. Its "first publish" section becomes a general recipe for bootstrapping a brand-new crate rather than a to-do item.

Still yours to do (needs a crates.io login, so I can't): link Trusted Publishing for termlens-cli → crates.io → termlens-cli → Settings → Trusted Publishing → GitHub, repository vyncint/termlens, workflow release.yml, environment release. Say the word afterwards and I'll delete publish-cli.yml and its zizmor entry; you delete the CARGO_REGISTRY_TOKEN secret. I've deliberately not removed the workflow yet — until the link exists it is the only working path for a termlens-cli release.

Refs #255