Snapper: no question on btrfs; vendor the SysGuides scripts

- On btrfs, snapshots + zstd compression now just happen (no prompt);
  --snapper=no remains the explicit opt-out.
- Vendor scripts/snapper-*.sh + config/snapper.actions from
  SysGuides/sysguides-snapper-fedora (MIT, upstream 0a28eb4) into
  vendor/snapper/ and install from there — no runtime clone of an
  external repo, and no dependency on exec bits (fixes the
  './install.sh: Permission denied' failure seen on the test VM).
- grub-btrfs still cloned at runtime from Antynea/grub-btrfs with the
  Fedora config applied; everything else is local now.

vendor/snapper/scripts/snapper-pre.sh

@@ -0,0 +1,45 @@
+#!/usr/bin/env bash
+set -e
+
+# snapper-pre.sh
+# ----------------
+# Creates a PRE snapshot before a DNF5 transaction begins.
+#
+# This script:
+# - Generates a description using snapper-desc.sh
+# - Stores the description and snapshot number in /run for later use
+#
+# The stored data is used by the POST script to:
+# - Pair snapshots correctly
+# - Improve snapshot descriptions (especially for GUI installs)
+#
+# Project: sysguides-snapper-fedora
+# Author: Madhu Desai (SysGuides)
+# Website: https://sysguides.com
+# GitHub: https://github.com/SysGuides/sysguides-snapper-fedora
+
+PID="$1"
+STATE_DIR="/run/snapper-actions"
+
+# Ensure runtime directory exists with secure permissions
+mkdir -p "$STATE_DIR"
+chmod 700 "$STATE_DIR"
+
+# On a fresh setup, DNF5 may fail with "filesystem error: cannot copy: packages.toml"
+# if this directory is missing, leaving an orphaned PRE snapshot with no POST.
+# This block ensures the directory exists before the transaction proceeds.
+if [[ ! -d /usr/lib/sysimage/libdnf5 ]]; then
+    mkdir -p /usr/lib/sysimage/libdnf5
+    restorecon -q /usr/lib/sysimage/libdnf5 2>/dev/null || true
+fi
+
+# Get transaction description (GUI or CLI command)
+desc=$(/usr/local/bin/snapper-desc.sh "$PID")
+
+# Store description for use in POST phase
+echo "$desc" > "$STATE_DIR/snapper_desc_${PID}"
+
+# Create PRE snapshot and store snapshot number
+pre=$(snapper -c root create -c number -t pre -p -d "$desc") || exit 1
+
+echo "$pre" > "$STATE_DIR/snapper_pre_${PID}"