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/Dockerfile

@@ -0,0 +1,20 @@
+# Runs host/lgtv-audiocap-receiver.py as a container instead of a systemd
+# unit — for setups (e.g. Unraid) where Docker is the native way to run
+# anything, but the ALSA loopback itself still has to be loaded on the real
+# host kernel first (see unraid/lgtv-audiocap-loopback.plg or
+# host/install-loopback.sh --method alsa, whichever fits the host).
+#
+# Build from the repo root, not this directory, so the image always tracks
+# the same receiver the systemd install path uses — no second copy to drift:
+#   docker build -f docker/Dockerfile -t lgtv-audiocap-receiver .
+FROM alpine:3.20
+
+RUN apk add --no-cache python3 alsa-utils
+
+COPY host/lgtv-audiocap-receiver.py /usr/local/bin/lgtv-audiocap-receiver.py
+COPY docker/entrypoint.sh /entrypoint.sh
+RUN chmod +x /usr/local/bin/lgtv-audiocap-receiver.py /entrypoint.sh
+
+EXPOSE 5004/udp
+
+ENTRYPOINT ["/entrypoint.sh"]