Add docker syntax to all Docker files

Dockerfile

@@ -1,3 +1,4 @@
+# syntax=docker/dockerfile:1
 # Automatically generated by hassfest.
 #
 # To update, run python3 -m script.hassfest -p docker

Dockerfile.dev

@@ -1,3 +1,4 @@
+# syntax=docker/dockerfile:1
 FROM mcr.microsoft.com/vscode/devcontainers/base:debian
 
 SHELL ["/bin/bash", "-o", "pipefail", "-c"]

machine/generic-x86-64

@@ -1,3 +1,4 @@
+# syntax=docker/dockerfile:1
 # Automatically generated by hassfest.
 #
 # To update, run python3 -m script.hassfest -p docker

machine/green

@@ -1,3 +1,4 @@
+# syntax=docker/dockerfile:1
 # Automatically generated by hassfest.
 #
 # To update, run python3 -m script.hassfest -p docker

machine/khadas-vim3

@@ -1,3 +1,4 @@
+# syntax=docker/dockerfile:1
 # Automatically generated by hassfest.
 #
 # To update, run python3 -m script.hassfest -p docker

machine/odroid-c2

@@ -1,3 +1,4 @@
+# syntax=docker/dockerfile:1
 # Automatically generated by hassfest.
 #
 # To update, run python3 -m script.hassfest -p docker

machine/odroid-c4

@@ -1,3 +1,4 @@
+# syntax=docker/dockerfile:1
 # Automatically generated by hassfest.
 #
 # To update, run python3 -m script.hassfest -p docker

machine/odroid-m1

@@ -1,3 +1,4 @@
+# syntax=docker/dockerfile:1
 # Automatically generated by hassfest.
 #
 # To update, run python3 -m script.hassfest -p docker

machine/odroid-n2

@@ -1,3 +1,4 @@
+# syntax=docker/dockerfile:1
 # Automatically generated by hassfest.
 #
 # To update, run python3 -m script.hassfest -p docker

machine/qemuarm-64

@@ -1,3 +1,4 @@
+# syntax=docker/dockerfile:1
 # Automatically generated by hassfest.
 #
 # To update, run python3 -m script.hassfest -p docker

machine/qemux86-64

@@ -1,3 +1,4 @@
+# syntax=docker/dockerfile:1
 # Automatically generated by hassfest.
 #
 # To update, run python3 -m script.hassfest -p docker

machine/raspberrypi3-64

@@ -1,3 +1,4 @@
+# syntax=docker/dockerfile:1
 # Automatically generated by hassfest.
 #
 # To update, run python3 -m script.hassfest -p docker

machine/raspberrypi4-64

@@ -1,3 +1,4 @@
+# syntax=docker/dockerfile:1
 # Automatically generated by hassfest.
 #
 # To update, run python3 -m script.hassfest -p docker

machine/raspberrypi5-64

@@ -1,3 +1,4 @@
+# syntax=docker/dockerfile:1
 # Automatically generated by hassfest.
 #
 # To update, run python3 -m script.hassfest -p docker

machine/yellow

@@ -1,3 +1,4 @@
+# syntax=docker/dockerfile:1
 # Automatically generated by hassfest.
 #
 # To update, run python3 -m script.hassfest -p docker

script/hassfest/docker.py

@@ -13,7 +13,8 @@ _GO2RTC_SHA = (
     "675c318b23c06fd862a61d262240c9a63436b4050d177ffc68a32710d9e05bae"  # 1.9.14
 )
 
-DOCKERFILE_TEMPLATE = r"""# Automatically generated by hassfest.
+DOCKERFILE_TEMPLATE = r"""# syntax=docker/dockerfile:1
+# Automatically generated by hassfest.
 #
 # To update, run python3 -m script.hassfest -p docker
 ARG BUILD_FROM
@@ -99,7 +100,8 @@ _MACHINES = {
     "yellow": _MachineConfig(arch="aarch64", packages=("raspberrypi-utils",)),
 }
 
-_MACHINE_DOCKERFILE_TEMPLATE = r"""# Automatically generated by hassfest.
+_MACHINE_DOCKERFILE_TEMPLATE = r"""# syntax=docker/dockerfile:1
+# Automatically generated by hassfest.
 #
 # To update, run python3 -m script.hassfest -p docker
 ARG BUILD_FROM=ghcr.io/home-assistant/{arch}-homeassistant:latest
@@ -126,7 +128,8 @@ def _generate_machine_dockerfile(
     )
 
 
-_HASSFEST_TEMPLATE = r"""# Automatically generated by hassfest.
+_HASSFEST_TEMPLATE = r"""# syntax=docker/dockerfile:1
+# Automatically generated by hassfest.
 #
 # To update, run python3 -m script.hassfest -p docker
 FROM python:3.14-alpine

script/hassfest/docker/Dockerfile

@@ -1,3 +1,4 @@
+# syntax=docker/dockerfile:1
 # Automatically generated by hassfest.
 #
 # To update, run python3 -m script.hassfest -p docker