Apply conversation bot improvements (proto-improvements)

Diff vs working-copy baseline = exactly this session's bot edits:
- constants.py: env-var config, safe JSON loading, optional-dependency
  guards, env->netrc token resolution, API_SHARED_KEY + service_headers()
- communication_subroutine.py: queue get(timeout) + Empty handling,
  daemon threads, cooperative stop_event, inbound _authorize_request()
- bot.py: single asyncio event loop with cooperative shutdown
- music_functions / radio_commands / librarian_commands: send
  X-Conjurer-Api-Key on internal HTTP calls via service_headers()

Musician runtime data overlay dropped; conjurer_musician/.gitignore now
keeps generated playlists/mp3 out of the repo. The 1+2+3 musician code
port already lives in the base conjurer_musician.

Depends on #9: must merge after restructure/working-copy-root.

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

music_functions.py

@@ -17,10 +17,13 @@ from constants import (
     SEND_MP3,
     SPOTIFY_CTRL,
     YOUTUBE_AUTH,
+    service_headers,
 )
 from spotify_dl import spotify
 from spotify_dl import youtube as youtube_download
 
+SERVICE_HEADERS = service_headers()
+
 
 
 class MusicFileList(object):
@@ -43,7 +46,11 @@ class MusicFileList(object):
         """
         try:
             self.logger.info("Attempt to connect to file service")
-            response = requests.get(f"{FILE_SERVICE_ADDRESS}{GET_MP3}", timeout=360)
+            response = requests.get(
+                f"{FILE_SERVICE_ADDRESS}{GET_MP3}",
+                headers=SERVICE_HEADERS,
+                timeout=360,
+            )
             self.music_file_list = response.json()["music_file_list"]
             self.file_service_active = True
         except requests.exceptions.RequestException as e:
@@ -98,7 +105,12 @@ class MusicFileList(object):
         """
         self.music_file_list.append(item)
         post_data = {"item": str(item)}
-        requests.post(f"{FILE_SERVICE_ADDRESS}{SEND_MP3}", json=post_data, timeout=360)
+        requests.post(
+            f"{FILE_SERVICE_ADDRESS}{SEND_MP3}",
+            json=post_data,
+            headers=SERVICE_HEADERS,
+            timeout=360,
+        )
 
 
 MUSIC_FILE_LIST = MusicFileList("discord")
@@ -308,6 +320,7 @@ async def search_music(ctx, how_many=0, slowa_kluczowe=None):
         requests.post,
         f"{FILE_SERVICE_ADDRESS}{GET_PLAYLIST}",
         json=jrequest,
+        headers=SERVICE_HEADERS,
         timeout=360,
     )
     return_data = await coroutine