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-wal-checkpoint.sh

@@ -0,0 +1,47 @@
+#!/usr/bin/env bash
+
+# snapper-wal-checkpoint.sh
+# --------------------------
+# Forces an SQLite WAL checkpoint for the RPM database used by libdnf5.
+#
+# Fedora 44 introduced DNF5 (libdnf5), which uses SQLite with WAL mode.
+# This can lead to inconsistencies during snapper undochange, where:
+# - Files are reverted correctly
+# - But the RPM database still reports packages as installed
+#
+# This script attempts to flush WAL data to the main database file
+# before the POST snapshot is created.
+#
+# The operation is best-effort:
+# - Retries multiple times if the database is busy
+# - Fails silently if unable to complete
+#
+# Project: sysguides-snapper-fedora
+# Author: Madhu Desai (SysGuides)
+# Website: https://sysguides.com
+# GitHub: https://github.com/SysGuides/sysguides-snapper-fedora
+
+python3 - <<'EOF'
+import sqlite3
+import time
+import sys
+
+DB = "/usr/lib/sysimage/rpm/rpmdb.sqlite"
+
+# Try up to 10 times to checkpoint WAL (single process, no respawn overhead)
+for i in range(10):
+    try:
+        conn = sqlite3.connect(DB, timeout=3)
+        conn.execute("PRAGMA busy_timeout=3000")
+        result = conn.execute("PRAGMA wal_checkpoint(TRUNCATE)").fetchone()
+        conn.close()
+        # result[1] = number of remaining frames in WAL (0 = fully flushed)
+        if result and result[1] == 0:
+            sys.exit(0)
+    except sqlite3.OperationalError:
+        pass
+    time.sleep(0.5)
+
+# Best-effort fallback
+sys.exit(1)
+EOF