chore(ci): pin ruff version in nox and nightly workflow

Ensures linting uses the same ruff version range in CI and nightly
jobs to avoid rule drift from latest releases.

.forgejo/workflows/nightly-quality.yml

@@ -10,6 +10,7 @@ on:
 env:
   UV_VERSION: "0.8.0"
   PYTHON_VERSION: "3.13"
+  RUFF_VERSION: ">=0.15,<0.16"
 
 jobs:
   full-quality-suite:
@@ -31,6 +32,10 @@ jobs:
         run: |
           uv pip install --system -e ".[dev,tests]"
 
+      - name: Ensure pinned ruff version
+        run: |
+          uv pip install --system "ruff${{ env.RUFF_VERSION }}"
+
       - name: Install behave-parallel
         run: |
           pip install -q behave-parallel

noxfile.py

@@ -311,14 +311,14 @@ setup(
 @nox.session(python=DEFAULT_PYTHON, reuse_venv=True, venv_backend="uv")
 def lint(session: nox.Session):
     """Check code formatting and linting."""
-    session.install("ruff")
+    session.install("ruff>=0.15,<0.16")
     session.run("ruff", "check", "src/", "scripts/", "examples/", "features/", "robot/")
 
 
 @nox.session(python=DEFAULT_PYTHON, reuse_venv=True, venv_backend="uv")
 def format(session: nox.Session):
     """Format code with ruff. Pass --check to verify without modifying."""
-    session.install("ruff")
+    session.install("ruff>=0.15,<0.16")
     session.run("ruff", "format", *session.posargs, ".")