Use the python version from .pyton-version file for hassfest image (#168368)

script/hassfest/docker.py

@@ -127,7 +127,7 @@ def _generate_machine_dockerfile(
 _HASSFEST_TEMPLATE = r"""# Automatically generated by hassfest.
 #
 # To update, run python3 -m script.hassfest -p docker
-FROM python:3.14-alpine
+FROM python:{python_version}-alpine
 
 ENV \
     UV_SYSTEM_PYTHON=true \
@@ -166,6 +166,11 @@ LABEL "com.github.actions.color"="gray-dark"
 """
 
 
+def _get_python_version(root: Path) -> str:
+    """Extract the Python version from .python-version."""
+    return (root / ".python-version").read_text(encoding="UTF-8").strip()
+
+
 @dataclass
 class File:
     """File."""
@@ -194,7 +199,9 @@ def _generate_files(config: Config) -> list[File]:
             config.root / "Dockerfile",
         ),
         File(
-            _HASSFEST_TEMPLATE.format(),
+            _HASSFEST_TEMPLATE.format(
+                python_version=_get_python_version(config.root),
+            ),
             config.root / "script/hassfest/docker/Dockerfile",
         ),
     ]

script/hassfest/docker/Dockerfile

@@ -1,7 +1,7 @@
 # Automatically generated by hassfest.
 #
 # To update, run python3 -m script.hassfest -p docker
-FROM python:3.14-alpine
+FROM python:3.14.2-alpine
 
 ENV \
     UV_SYSTEM_PYTHON=true \