split: betoniarka (radio operator) colocated with liquidsoap; musician goes Discord-only

Permissions post-mortem that motivated this: the musician wrote radio
playlists AS ROOT onto a ROOT-OWNED network share which liquidsoap then
read AS USER 'radio' - chown fails on such shares by design (root squash /
uid mapping), so the radio came up and died on the playlists. The fix is
structural: the playlist WRITER now lives in the same container as the
READER, as the same user, on a local volume. No shared partition, no
chown, no uid mapping.

New: conjurer_betoniarka/betoniarka.py - runs inside the radio container
(started by the entrypoint as user 'radio', port 5005):
- library scan -> all_playlist/hit playlists with LOCAL container paths
  (start + every 24h + authenticated GET /rescan)
- bot-facing radio API moved from the musician: /add_to_priority,
  /create_priority_playlist, /request_radio_file, /clear_pr_pls,
  plus GET /ping (health) and /stream (web page)
- radio_log/persistence tailer forwarding play events to the bot's
  /prepped_tracks with the shared API key (bot-unreachable = logged, not fatal)

Musician: pure Discord music player now - keeps /mp3, /update_mp3,
/get_music and the file-share endpoints; all radio playlist writing, radio
paths/env and the tailer removed.

Bot: new CONJURER_RADIO_SERVICE (defaults to CONJURER_FILE_SERVICE so
un-split deployments keep working); radio_commands targets it; separate
'radio' health-gate group on betoniarka /ping (musician group now covers
music_commands + file_search_commands only).

Docker: betoniarka baked into the radio image (python3 + flask/waitress/
requests from Debian debs), port 5005 exposed, entrypoint starts it via
setpriv as 'radio'; data-volume chown is now best-effort with a loud
warning (keep the volume local); docs get the post-mortem + wiring.

Verified: py_compile everything; functional stub tests - rescan writes
local-path playlists, wyszukaj scores and appends to priority, auth
401/ok, tailer forward carries the API key.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docker/entrypoint.radio.sh

@@ -91,13 +91,23 @@ esac
 
 # Liquidsoap refuses to run as root (init: security exit), so hand the data
 # volume to the dedicated 'radio' user and drop privileges for the main
-# process. The script parses the icecast secret directly, so make that one
-# file group-readable for 'radio' (kept 640, root-owned).
-chown -R radio:radio "$DATA"
+# process. chown is best-effort: on local volumes it always works (the
+# supported layout); network filesystems with root-squash reject it, hence
+# the warning instead of a fatal abort.
+chown -R radio:radio "$DATA" 2>/dev/null \
+    || echo "WARNING: chown of $DATA failed (network FS?) - keep this volume LOCAL to the radio VM" >&2
 chgrp radio "$CREDS" 2>/dev/null && chmod 640 "$CREDS" || true
 if ! setpriv --reuid radio --regid radio --init-groups -- test -r "$MUSIC"; then
     echo "WARNING: music dir $MUSIC is not readable by the 'radio' user" >&2
 fi
 
+# Betoniarka: the radio-operator API + radio-log forwarder, running as the
+# SAME user as liquidsoap on the SAME volume - this is what makes the old
+# musician-writes-as-root-over-network-share permission mess go away.
+BETONIARKA_DATA="$DATA" BETONIARKA_MUSIC="$MUSIC" \
+    setpriv --reuid radio --regid radio --init-groups -- \
+    python3 /app/betoniarka.py &
+echo "betoniarka started (pid $!)"
+
 cd "$DATA"
 exec setpriv --reuid radio --regid radio --init-groups -- "$@"