fix: implement actual system reboot via shutdown/systemctl commands

- Fix reboot_system() to use shutdown -r +N for delayed reboots
- Fix patches handler to call reboot_system() instead of just logging
- Add CAP_SYS_BOOT capability to systemd service for LXC reboot support
- Remove unused warn import from packages/mod.rs
- Bump version to 0.3.1

configs/linux-patch-api.service

@@ -18,6 +18,9 @@ RuntimeDirectoryMode=0755
 
 # Security hardening
 NoNewPrivileges=true
+# Allow reboot capability for scheduled reboots
+CapabilityBoundingSet=CAP_SYS_BOOT
+AmbientCapabilities=CAP_SYS_BOOT
 # ProtectSystem removed - package management requires write access to /usr, /etc, /lib
 # Network security provided by mTLS + IP whitelist
 ProtectHome=true