Fix correlation false-merge, switch STT to whisper-1 without vocab prompt

- correlator: unit_overlap on dispatch channels now applies content
  divergence check when the call has geocoded coords but the incident
  doesn't; previously this gap caused unrelated calls to merge into
  stale incidents (e.g. patrol officer at a second scene 70 min later)
- STT: switch default model from gpt-4o-transcribe to whisper-1, which
  faithfully transcribes all exchanges in multi-PTT recordings; gpt-4o
  was silently dropping utterances, starving the correlation engine
- STT: remove vocabulary from the Whisper prompt; whisper-1 echoes
  prompted terms into noise/silence, skewing extracted incident data;
  vocabulary context is now applied exclusively in the GPT extraction
  step (build_gpt_vocab_block) where it is used as reference only

drb-c2-core/app/config.py

@@ -19,7 +19,7 @@ class Settings(BaseSettings):
 
     # OpenAI (STT + intelligence)
     openai_api_key: Optional[str] = None
-    stt_model: str = "gpt-4o-transcribe"  # whisper-1 | gpt-4o-mini-transcribe | gpt-4o-transcribe
+    stt_model: str = "whisper-1"  # whisper-1 | gpt-4o-mini-transcribe | gpt-4o-transcribe
 
     # Google Maps (geocoding)
     google_maps_api_key: Optional[str] = None