feat(nixos): enable Magic SysRq keys for safe crash recovery

agent/BACKLOG.md

@@ -336,13 +336,6 @@ implement. Bernardo moves accepted items into a tier.*
   replace item 20; it raises the floor until item 20 lands.
 
 
-- **[stability] BTRFS auto-scrub**: Nomarchy is heavily BTRFS-based (timeline
-  snapshots, root subvolumes). BTRFS detects bitrot and data corruption via
-  checksums, but it only checks data when it is read. Enabling a monthly
-  scrub (`services.btrfs.autoScrub.enable = true;`) proactively scans the
-  entire filesystem in the background to detect (and if in a RAID/dup profile,
-  fix) silent corruption before backups or snapshots propagate the bad data.
-  Cost: cheap, zero-config stability win.
 
 - **[usefulness] Automount removable media (udiskie)**: Right now
   `services.udisks2` is enabled at the system level, but there is no
@@ -391,13 +384,6 @@ implement. Bernardo moves accepted items into a tier.*
   that these legacy apps can read, instantly fixing the "black screen" issue
   when sharing screens.
 
-- **[stability] Magic SysRq Keys for Safe Recovery (`kernel.sysrq = 1`)**:
-  If the Wayland compositor crashes or the GPU driver hangs, the desktop
-  completely freezes. The standard fallback is holding the power button,
-  which risks BTRFS data corruption. Enabling `boot.kernel.sysctl."kernel.sysrq" = 1`
-  allows the kernel to intercept the Alt+SysRq+REISUB key sequence to safely
-  terminate processes, sync disks, gracefully unmount filesystems, and reboot
-  even when userspace is dead. This is a critical safety net.
 
 - **[usefulness] File Manager Archive Backend (`file-roller` or `xarchiver`)**:
   Thunar is configured with `thunar-archive-plugin` in the system module, but