ci(prepare-release): drop the uv.lock pre-flight — this repo has no lockfile

[CSSFrancis]

The first real run
of Prepare Release died at step 6:

error: Unable to find lockfile at `uv.lock`, but `--check` was provided.

uv.lock is on line 11 of .gitignore and has never been tracked. I took the
step from SpyDE's Prepare Release and checked it against a working tree where
uv sync had left a lockfile lying around, rather than against what git
actually carries. A git ls-files would have caught it.

It does not belong here anyway

SpyDE is an application: it ships its lock in the installer payload, and the
user's sidecar env is resolved from it on their machine, so drift reaches users.
de-shell is a library on PyPI — the apps resolve their own environments, and
a lockfile here would mean nothing to them. The comment I wrote justifying the
step actually described SpyDE's lock, which SpyDE already checks.

The other pre-flight stays: the git-deps-pinned grep reads pyproject.toml and
needs no lockfile.

Two claims in the generated PR body were also wrong

• It said the lock check had passed. Removed.
• It told the reviewer to confirm CI passes — but CI does not start on its own
  for a PR opened with GITHUB_TOKEN. GitHub suppresses workflow runs for
  events raised with that token, so the release PR gets no pull_request run at
  all. The checklist now says so, and says to close/reopen the PR or push an
  empty commit to get one.

Dry run

Rather than eyeball it again, I cloned main into a pristine workspace — no
.venv, no lockfile, nothing installed — and ran every step by hand:

step	result
Compute new version	reads 0.2.2 from de_shell/__init__.py
Verify git deps pinned	pass (none present)
Bump + read-back guard	__version__ → 0.3.0, guard confirms
towncrier draft + build	OK — needs no de_shell import when --version is passed
Commit release changes	stages the bump, the new section, and 3 consumed fragments

The assembled 0.3.0 section came out right: #2 under Bug Fixes, #7 and the
towncrier setup under Maintenance.

No cleanup needed from the failed run — it died before the bump, so nothing was
pushed and no release/* branch was left behind.