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

@@ -0,0 +1,35 @@
+#!/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"
+}