Migrate LMS/Squeezelite addon; fix is_service_enabled dead pre-check; bump to v2.9.0

New menus/addon_lms_squeezelite.sh: install/reconfigure/uninstall for an
LMS (Lyrion/Logitech Media Server) server and a Squeezelite player,
wired into install.sh's Addons menu. Squeezelite's own start script and
systemd unit now go through $BIN_DIR/$SYSTEMD_DIR like every other
addon instead of hardcoded /usr/local/bin and /etc/systemd/system; LMS's
own apt repo/GPG key/ufw rules stay at their real fixed system paths,
same approach as CUPS.

Fixed a real unguarded-pipeline bug from the legacy install_lms():
`sudo systemctl enable "$service_name" 2>&1 | tee ...` made the exit
status depend on tee (always 0) instead of systemctl enable, silently
swallowing real enable/start failures. Now uses enable_and_start_units().

Fixed is_service_enabled() (shared helper, backported into the legacy
script too): its list-unit-files pre-check never matched a bare service
name, so it always fell through to "not enabled" regardless of the real
state. Dropped the dead pre-check.

Full command-level stubbed test suite covering install/reconfigure/
uninstall for both LMS and Squeezelite, including the repo-vs-fallback-
download path, undetectable-service-name path, and enable/start-failure
path. Full 12-suite regression + real end-to-end menu navigation via
install.sh all pass.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VfsFSoRqfbRG7XAg5RoE7e

lib/config.sh

@@ -78,6 +78,20 @@ is_service_active() {
     systemctl is-active --quiet "$service" 2>/dev/null
 }
 
+# Whether a service is enabled (would start on boot), regardless of
+# whether it's currently running. The legacy script's version of this
+# pre-checked `systemctl list-unit-files | grep -q "^${service}\s"`
+# before calling is-enabled - but every call site passes a bare service
+# name (e.g. "squeezelite"), while list-unit-files lines start with
+# "squeezelite.service", so that regex never matched and the legacy
+# function always fell through to `return 1` no matter the real state.
+# `systemctl is-enabled` already reports "not found" as a failure on its
+# own, so the pre-check was both broken and unnecessary - dropped here.
+is_service_enabled() {
+    local service="$1"
+    systemctl is-enabled --quiet "$service" 2>/dev/null
+}
+
 # Load every setting config.json has into the bash globals above.
 # Safe to call with no existing config file - leaves script defaults in place.
 load_existing_config() {