feat(raspberrypi): add Raspberry Pi configuration section

Documents and scripts to reproduce the IPA integration on the Pi
(raspberrypi.tail13f623.ts.net, Debian 12 bookworm):

- setup-ipa-sudo.sh: writes /etc/sudoers.d/ipa-admins granting
  %admins NOPASSWD:ALL (same IPA admins group as pbs/pdm/pve1)
- setup-docker-ipa-gid.sh: pins local docker group GID to 50010
  via groupmod --non-unique so IPA docker-access group membership
  alone grants docker socket access (mirrors NixOS lib.mkForce approach)
- README.md + CLAUDE.md: quick-start, current status, guardrails

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

raspberrypi/scripts/lib/common.sh

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+#!/bin/bash
+# Shared helpers for raspberrypi scripts. Sourced, not executed directly:
+#   SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+#   source "${SCRIPT_DIR}/lib/common.sh"
+
+require_root() {
+    if [ "$(id -u)" -ne 0 ]; then
+        echo "Must run as root." >&2
+        exit 1
+    fi
+}
+
+# backup_file <path>
+# Copies an existing file to <path>.bak.<epoch>. No-op if it doesn't exist.
+backup_file() {
+    local path="$1"
+    if [ -f "$path" ]; then
+        cp "$path" "${path}.bak.$(date +%s)"
+        echo "Backed up ${path}"
+    fi
+}
+
+# write_if_changed <path> <content>
+# Writes content to path only if it differs from what's already there,
+# backing up the previous version first. Prints what happened.
+write_if_changed() {
+    local path="$1" content="$2"
+    if [ -f "$path" ] && [ "$(cat "$path")" = "$content" ]; then
+        echo "Already up to date: $path"
+        return 0
+    fi
+    backup_file "$path"
+    printf '%s\n' "$content" > "$path"
+    echo "Wrote $path"
+}

raspberrypi/scripts/setup-docker-ipa-gid.sh

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+#!/bin/bash
+# Pin the local 'docker' group GID to match the IPA 'docker-access' group
+# (GID 50010) so that IPA group membership alone grants docker socket access.
+#
+# On Debian, GID 50010 is already present via SSSD (the IPA group), so
+# groupmod requires --non-unique to allow the local docker group to share
+# it. The docker.socket + docker.service pair must be fully stopped before
+# removing the stale socket so systemd recreates it with the new GID.
+#
+# Idempotent — exits 0 without touching anything if the GID is already 50010.
+#
+# Run as root after setup-ipa-sudo.sh has been applied and docker is running.
+#
+# Usage: sudo ./setup-docker-ipa-gid.sh
+set -euo pipefail
+
+DOCKER_ACCESS_GID=50010
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+# shellcheck source=lib/common.sh
+source "${SCRIPT_DIR}/lib/common.sh"
+require_root
+
+if ! command -v docker &>/dev/null; then
+    echo "ERROR: docker not found -- install Docker before running this script." >&2
+    exit 1
+fi
+
+current_gid=$(getent group docker | cut -d: -f3)
+if [ "$current_gid" = "$DOCKER_ACCESS_GID" ]; then
+    echo "docker group is already GID ${DOCKER_ACCESS_GID} -- nothing to do."
+    exit 0
+fi
+
+echo "Changing docker group GID: ${current_gid} -> ${DOCKER_ACCESS_GID}"
+
+# SSSD exposes GID 50010 via the IPA docker-access group, so groupmod sees
+# it as already in use. --non-unique lets the local docker group share it.
+groupmod --non-unique -g "${DOCKER_ACCESS_GID}" docker
+
+echo "Restarting docker to recreate socket with new GID..."
+systemctl stop docker.service docker.socket
+rm -f /var/run/docker.sock
+systemctl start docker.socket docker.service
+
+actual_gid=$(stat -c '%g' /var/run/docker.sock)
+if [ "$actual_gid" != "$DOCKER_ACCESS_GID" ]; then
+    echo "ERROR: socket GID is ${actual_gid}, expected ${DOCKER_ACCESS_GID}" >&2
+    exit 1
+fi
+
+echo "Done. Docker socket is now GID ${DOCKER_ACCESS_GID} (docker / docker-access)."
+echo "IPA members of the 'docker-access' group can now run docker without explicit local group membership."

raspberrypi/scripts/setup-ipa-sudo.sh

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+#!/bin/bash
+# Grant the IPA 'admins' group passwordless sudo on this Raspberry Pi.
+#
+# Writes /etc/sudoers.d/ipa-admins with NOPASSWD: ALL for the admins group.
+# Idempotent — safe to re-run.
+#
+# Run as root (or via the local 'raspi' user's NOPASSWD sudo) after
+# ipa-client-install has been completed and SSSD is active.
+#
+# Usage: sudo ./setup-ipa-sudo.sh
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+# shellcheck source=lib/common.sh
+source "${SCRIPT_DIR}/lib/common.sh"
+require_root
+
+if [ ! -f /etc/ipa/default.conf ]; then
+    echo "ERROR: /etc/ipa/default.conf not found -- is this host enrolled in FreeIPA?" >&2
+    exit 1
+fi
+
+write_if_changed /etc/sudoers.d/ipa-admins '%admins ALL=(ALL) NOPASSWD:ALL'
+chmod 0440 /etc/sudoers.d/ipa-admins
+
+visudo -c >/dev/null
+echo "Sudoers file valid. IPA admins group has NOPASSWD sudo on this host."