Let the Device field be picked, not typed blind

Diagnosing capture on a real TV meant reading pactlSources off the
screen and typing an exact PulseAudio source name back in through the
same remote-driven text field — no way to copy-paste, easy to
mistype, and the one piece of information (which source, if any, is
actually RUNNING) was buried in a JSON dump.

Added two choice() pickers bound to the same capture.device setting:
one built from pactlSources (pulse/auto backends), one built from
alsaCapturePcms (alsa backend), both parsed from diagnostics the
service already collects — no new Luna method needed. Diagnostics
already run once at boot, so the picker is populated immediately,
before the user ever presses "Run diagnostics" by hand.

Picking a value writes straight into capture.device, and the plain
text field stays as the fallback for anything the parser misses.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

docker/entrypoint.sh

@@ -0,0 +1,23 @@
+#!/bin/sh
+# Maps environment variables onto lgtv-audiocap-receiver.py's flags, since
+# that's how Unraid (and most container UIs) expose configuration — nobody
+# wants to hand-edit a CLI in the "extra parameters" box.
+set -eu
+
+args="--port ${PORT:-5004} --bind ${BIND:-0.0.0.0}"
+args="$args --output ${OUTPUT:-aplay} --device ${DEVICE:-hw:Loopback,0,0}"
+args="$args --rate ${RATE:-48000} --channels ${CHANNELS:-2}"
+args="$args --latency-ms ${LATENCY_MS:-80} --prebuffer-ms ${PREBUFFER_MS:-60}"
+args="$args --max-gap ${MAX_GAP:-200} --reset-after ${RESET_AFTER:-5.0}"
+args="$args --stats ${STATS:-30}"
+
+[ -n "${MULTICAST:-}" ] && args="$args --multicast $MULTICAST"
+[ -n "${IFACE:-}" ] && args="$args --iface $IFACE"
+[ "${FILL_SILENCE:-1}" = "0" ] && args="$args --no-fill-silence"
+
+# Anything passed on the "docker run" command line (or Unraid's "Extra
+# Parameters") is appended last, so it can override an env-derived flag —
+# and so plain `--help` works instead of silently starting the daemon.
+echo "lgtv-audiocap-receiver.py $args $*"
+# shellcheck disable=SC2086
+exec python3 /usr/local/bin/lgtv-audiocap-receiver.py $args "$@"