feat(nas): update to 25.11, add software, add storage plan

hosts/nas/STORAGE.md

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+# NAS Storage Notes
+
+## Current Issue: XFS Metadata Overhead
+
+The XFS filesystem on `/var/lib/multimedia` uses ~100GB more than the actual file data due to metadata overhead.
+
+### Root Cause
+
+The filesystem was created with advanced features enabled:
+
+```
+rmapbt=1    # Reverse mapping btree - tracks block ownership
+reflink=1   # Copy-on-write support
+```
+
+These features add metadata that scales with **filesystem size**, not file count. On a 5TB filesystem with 700GB of data, this results in ~100GB (~2%) overhead.
+
+### Diagnostic Commands
+
+```bash
+# Compare file data vs filesystem usage
+du -sh /var/lib/multimedia           # Actual file data
+df -h /var/lib/multimedia            # Filesystem reports
+
+# Check XFS features
+xfs_info /var/lib/multimedia
+
+# Verify block allocation
+xfs_db -r -c "freesp -s" /dev/mapper/vg--data-lv--multimedia
+```
+
+## Recommendation: LVM + ext4
+
+For media storage (write-once, read-many), ext4 with minimal reserved space offers the lowest overhead:
+
+```bash
+# Create filesystem with 0% reserved blocks
+mkfs.ext4 -m 0 /dev/vg/lv
+
+# Or adjust existing ext4
+tune2fs -m 0 /dev/vg/lv
+```
+
+### Why ext4 over XFS for this use case
+
+| Consideration | ext4 | XFS (current) |
+|---------------|------|---------------|
+| Reserved space | 0% with `-m 0` | N/A |
+| Metadata overhead | ~0.5% | ~2% (with rmapbt) |
+| Shrink support | Yes | No |
+| Performance for 4K stream | Identical | Identical |
+
+A single 4K remux stream requires ~12 MB/s. Any filesystem handles this trivially.
+
+## Migration Path
+
+1. Backup data from XFS volumes
+2. Recreate LVs with ext4 (`mkfs.ext4 -m 0`)
+3. Restore data
+4. Update `/etc/fstab` or NixOS `fileSystems` config