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>

librarian_commands.py

@@ -15,7 +15,9 @@ from discord.ext import commands, tasks
 
 from ai_functions import handle_response
 from communication_subroutine import IN_COMM_Q, OUT_COMM_Q, QueryControl
-from constants import DIR_PATH_SADOX, LIBRARIAN_SERVICE_ADDRESS, SEND_QUERY
+from constants import DIR_PATH_SADOX, LIBRARIAN_SERVICE_ADDRESS, SEND_QUERY, service_headers
+
+SERVICE_HEADERS = service_headers()
 
 
 class DataModule(commands.Cog):
@@ -165,6 +167,7 @@ class DataModule(commands.Cog):
             requests.post,
             f"{LIBRARIAN_SERVICE_ADDRESS}{SEND_QUERY}",
             json=json_query,
+            headers=SERVICE_HEADERS,
             timeout=360,
         )
         await ctx.send(
@@ -260,6 +263,7 @@ class DataModule(commands.Cog):
             requests.post,
             f"{LIBRARIAN_SERVICE_ADDRESS}{SEND_QUERY}",
             json=json_query,
+            headers=SERVICE_HEADERS,
             timeout=360,
         )
         await ctx.send(