Enforce dependency freshness in utils' own CI

Deliberately the last step, not the first. All eleven manifests here are now
on latest stable -- four Dart libs, two Python packages, two TypeScript
packages -- so `--all --strict` exits 0 and this can be a gate rather than a
permanent red light. Installing it any earlier would have taught everyone to
ignore it.

Unlike every other repo's copy, this one runs `scripts/check_dependency_freshness.sh`
directly instead of checking kuhyx/utils out into `.utils`: this repo IS the
gate.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CRykabMwPgDzFHcARoqpaK

.github/workflows/dependency-freshness.yml

@@ -0,0 +1,52 @@
+name: dependency freshness
+
+# Every dependency on its ecosystem's newest STABLE release, enforced on push
+# as well as at commit time. This repo OWNS the gate, so unlike every other
+# repo it runs its own copy directly instead of checking one out.
+#
+# Deliberately added last, after all eleven manifests here were brought
+# current: installing the gate on a repo before its dependencies are upgraded
+# makes it instantly and permanently red, which teaches people to ignore it. The local pre-commit hook only sees the manifests
+# in a commit and can be skipped entirely by a fresh clone that never ran
+# `pre-commit install`; this runs `--all` over the whole repo.
+#
+# `--strict` is CI-only. Offline the gate degrades to its cached answer and
+# passes, because `--no-verify` is banned locally and a hook that hard-failed
+# on a flaky connection would leave no way to commit. A runner is always
+# online, so here an undeterminable answer is a real failure.
+#
+# Expect this to go red for reasons this repo's commit did not cause: an
+# upstream release overnight is enough. That is the chosen behaviour -- the
+# alternative is a gate that only notices staleness when someone remembers to
+# look.
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+  workflow_dispatch:
+
+jobs:
+  dependency-freshness:
+    name: dependencies on newest stable
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.13"
+
+      - name: Install the gate's two runtime dependencies
+        run: python -m pip install --upgrade pyyaml packaging
+
+      - name: Cache registry lookups
+        uses: actions/cache@v4
+        with:
+          path: ~/.cache/dep-freshness
+          key: dep-freshness-${{ hashFiles('**/pubspec.yaml', '**/package.json', '**/requirements*.txt', '**/pyproject.toml') }}
+          restore-keys: dep-freshness-
+
+      - name: Every dependency is on newest stable
+        run: bash scripts/check_dependency_freshness.sh --all --strict