feat: consolidate LG TV bridge — cached IP discovery, robust WoL, systemd deploy

Rework the MQTT bridge into a single deployable unit:
- Drop the self-SSH hop; run locally on steel141 (on the TV's LAN, has
  bscpylgtv, effectively always-on).
- Cache last-known TV IP and probe it directly; /24 ping-sweep only on a
  cache miss. Stops the 30s HA state poll from flapping/spamming the net.
- WoL now unicast (last-known IP) + broadcast, ports 9/7, 3 bursts.
- systemd unit (User=seth, EnvironmentFile for MQTT_PASSWORD), install.sh,
  env template, .gitignore. Removes the half-finished lgtv.sh.new.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.gitignore

@@ -0,0 +1,6 @@
+.backup/
+__pycache__/
+*.pyc
+*.new
+lgtv.env
+.env