feat: add call history API endpoints and TTS service client

Adds read-only access to persisted call records for the dashboard
and implements a client for the Rhema text-to-speech service.

- api/call_history.py: New router providing paged call lists
  and detailed call records with transcript metadata.
- services/tts.py: Async client for OpenAI-compatible TTS
  endpoints (Rhema/Kokoro) used for call-flow steps.

models/events.py

@@ -32,6 +32,19 @@ class EventType(str, Enum):
     # Audio
     AUDIO_CLASSIFIED = "audio.classified"
     TRANSCRIPT_CHUNK = "audio.transcript_chunk"
+    SPEAK_PLAYED = "audio.speak_played"
+
+    # AI Receptionist
+    RECEPTIONIST_GREETING = "receptionist.greeting"
+    RECEPTIONIST_LISTENING = "receptionist.listening"
+    RECEPTIONIST_CAPTURED_INTENT = "receptionist.captured_intent"
+    RECEPTIONIST_ROUTING = "receptionist.routing"
+    RECEPTIONIST_MESSAGE_SAVED = "receptionist.message_saved"
+    RECEPTIONIST_REJECTED = "receptionist.rejected"
+
+    # Routing
+    ROUTING_RULE_MATCHED = "routing.rule_matched"
+    ROUTING_DEVICE_DND = "routing.device_dnd"
 
     # Device
     DEVICE_REGISTERED = "device.registered"