scaffold: aports overlay, build script, CI workflow, README

Kernel aport forked from pmaports 7.1.2-r0, repointed at milos-linux
combined-stable with the tested FP6 config (+EFI_ZBOOT for packaging);
imsd + nftables aports from the pending pmaports submission. build.sh
carries TODO(validate) markers - not yet run end-to-end.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

build.sh

@@ -0,0 +1,63 @@
+#!/bin/sh -eu
+# fp6-img pipeline: build a flashable postmarketOS image for the Fairphone 6
+# with the Catcrafts kernel (milos-linux combined-stable) and imsd (VoLTE).
+#
+# Runs in CI inside an Alpine container on a privileged runner (pmbootstrap
+# needs loop devices; the aarch64 chroots need qemu-user binfmt on the host).
+# Also runnable locally in any Alpine environment with the same privileges.
+#
+# Status: SCAFFOLD — steps marked TODO(validate) have not run end-to-end yet.
+
+KERNEL_REPO=https://forgejo.catcrafts.net/Catcrafts/milos-linux.git
+KERNEL_BRANCH=combined-stable
+KERNEL_APORT=aports/device/linux-postmarketos-qcom-milos
+
+cd "$(dirname "$0")"
+
+apk add -q pmbootstrap git zstd
+
+# --- 1. Pin the kernel source ------------------------------------------------
+# Source archives are disabled on the Forgejo instance, so generate the
+# tarball ourselves and let abuild treat it as a local source file.
+rm -rf /tmp/milos-src "$KERNEL_APORT"/milos-linux-*.tar.gz
+git clone --depth=1 -b "$KERNEL_BRANCH" "$KERNEL_REPO" /tmp/milos-src
+COMMIT=$(git -C /tmp/milos-src rev-parse HEAD)
+git -C /tmp/milos-src archive --prefix=milos-linux/ \
+    -o "$PWD/$KERNEL_APORT/milos-linux-$COMMIT.tar.gz" HEAD
+sed -i "s/^_commit=.*/_commit=\"$COMMIT\"/" "$KERNEL_APORT/APKBUILD"
+
+# --- 2. Configure pmbootstrap ------------------------------------------------
+# TODO(validate): exact non-interactive init + overlay ordering (our aports
+# dir must shadow the upstream pmaports aports of the same name).
+pmbootstrap config device fairphone-fp6
+pmbootstrap config ui plasma-mobile
+pmbootstrap config systemd always
+pmbootstrap config extra_packages imsd,postmarketos-config-nftables-imsd
+# TODO(validate): point pmbootstrap at "$PWD/aports" as an overlay.
+
+pmbootstrap checksum linux-postmarketos-qcom-milos
+pmbootstrap checksum imsd
+
+# --- 3. Build the image ------------------------------------------------------
+# Same default credentials as the official postmarketOS images.
+pmbootstrap -y zap || true
+pmbootstrap install --password 147147
+
+# --- 4. Collect artifacts ----------------------------------------------------
+# TODO(validate): exact export paths (boot.img + rootfs) for the fastboot
+# flash method on fairphone-fp6.
+rm -rf /tmp/pmos-export dist
+mkdir -p /tmp/pmos-export dist
+pmbootstrap export /tmp/pmos-export
+cp -L /tmp/pmos-export/boot.img dist/fp6-boot.img
+cp -L /tmp/pmos-export/*.img dist/ 2>/dev/null || true
+
+{
+    echo "kernel:        $KERNEL_REPO $KERNEL_BRANCH @ $COMMIT"
+    echo "built:         $(date -u +%Y-%m-%dT%H:%M:%SZ)"
+    echo "default login: user / 147147 (same as official postmarketOS images)"
+} > dist/build-info.txt
+cp README.md dist/README.md
+
+(cd dist && sha256sum -- * > sha256sums.txt)
+ls -la dist/