chore: open-source release-prep (udev flag, SPDX headers, boolean style)

Three release cleanups, all behavior-preserving for my machines:

- Gated the Logitech BRIO udev rule behind INSTALL_DEVICE_UDEV_RULES (default yes, opt-out), so the device-specific rule is off for anyone without that hardware. Added the config read, validation, and a conf.example entry.
- Added a GPL-3.0-or-later SPDX-License-Identifier header after the shebang of all 24 shell scripts in the repo.
- Standardized boolean conditionals on the explicit [ "$var" = "true" ] form, replacing the bare `if $var` idiom. The STEPS function-dispatch is left alone, since it runs a function name rather than testing a boolean.

1 files changed, 1 insertions, 0 deletions

diff --git a/init b/init
index a20bf7c..c300fea 100755
--- a/init
+++ b/init
@@ -1,4 +1,5 @@
 #!/bin/sh
+# SPDX-License-Identifier: GPL-3.0-or-later
 
 # update and install tmux and git
 pacman -Sy --noconfirm >> /dev/null