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>

bot.py

@@ -37,6 +37,7 @@ from constants import (
     GET_MP3,
     LIBRARIAN_SERVICE_ADDRESS,
     LOGFILE,
+    RADIO_SERVICE_ADDRESS,
     TOKEN,
 )
 
@@ -96,10 +97,15 @@ CORE_EXTENSIONS = [
 ]
 
 SERVICE_EXTENSION_GROUPS = {
-    # musician (file service): music download/search, radio control, file shares
+    # musician (file service): Discord music download/search, file shares
     "musician": {
         "health_url": f"{FILE_SERVICE_ADDRESS}{GET_MP3}",
-        "extensions": ["music_commands", "radio_commands", "file_search_commands"],
+        "extensions": ["music_commands", "file_search_commands"],
+    },
+    # betoniarka (radio operator colocated with Liquidsoap): radio playlists
+    "radio": {
+        "health_url": f"{RADIO_SERVICE_ADDRESS}/ping",
+        "extensions": ["radio_commands"],
     },
     # librarian: DOI / Crossref search
     "librarian": {