refactor: remove constants and put in config file

removed all constants from all files and put them in src/control_backend/core/config.py
also removed some old mock agents that we don't use anymore

ref: N25B-236

src/control_backend/agents/transcription/transcription_agent.py

@@ -31,9 +31,10 @@ class TranscriptionAgent(Agent):
     class Transcribing(CyclicBehaviour):
         def __init__(self, audio_in_socket: azmq.Socket):
             super().__init__()
+            max_concurrent_tasks = settings.transcription_settings.max_concurrent_transcriptions
             self.audio_in_socket = audio_in_socket
             self.speech_recognizer = SpeechRecognizer.best_type()
-            self._concurrency = asyncio.Semaphore(3)
+            self._concurrency = asyncio.Semaphore(max_concurrent_tasks)
 
         def warmup(self):
             """Load the transcription model into memory to speed up the first transcription."""