Add scripts and configuration files for mergerfs setup and testing

- Created backup files for wipefs on specific disk partitions.
- Added db-test script to verify metadata.db file integrity.
- Documented successful mergerfs branch and pool configurations in mfs-good.txt.
- Implemented mfs write test in mfs-test.txt.
- Included mergerfs version and device information in mfs.txt.
- Developed rebuild scripts for mergerfs stages, including verification and filesystem creation.
- Generated stage logs for each rebuild step to track disk and filesystem status.
- Added checks for systemd mount requirements and filesystem verification in stage4.

others/plex-books-unknown-check/README.TXT

@@ -0,0 +1,42 @@
+PLEX BOOKS UNKNOWN SECONDARY CHECK
+==================================
+
+This tool reads:
+
+  /mnt/recovery/plex-books-manifest.jsonl
+
+and inspects only entries previously classified UNKNOWN.
+
+It NEVER writes to the damaged ext4 filesystem.
+
+It uses debugfs catastrophic/read-only mode and classifies UNKNOWN files as:
+
+  ETB_LOST
+    One or more extent-tree metadata blocks live inside the known-dead PV.
+
+  ETB_SURVIVES
+    Extent-tree metadata blocks are outside the dead PV; investigate further.
+
+  EXTENTS_RECOVERABLE
+    The file now exposes parsable data extents and none overlap the dead PV.
+
+  DATA_OVERLAP
+    Parsable data extents overlap the dead PV.
+
+  OTHER_UNKNOWN
+    Metadata still cannot be interpreted.
+
+Known-dead filesystem blocks:
+
+  3418636288 - 4395389951
+
+Run:
+
+  mkdir -p /mnt/plexunk
+  mount -o ro LABEL=PLEXUNK /mnt/plexunk
+  bash /mnt/plexunk/CHECKUNK.SH
+
+Results are written to:
+
+  /mnt/recovery/plex-books-unknown-check.tsv
+  /mnt/recovery/plex-books-unknown-summary.txt