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.

config.py

@@ -76,6 +76,38 @@ class HoldSlayerSettings(BaseSettings):
     hold_check_interval: float = Field(default=2.0, validation_alias="HOLD_CHECK_INTERVAL")
 
 
+class TTSSettings(BaseSettings):
+    """Rhema TTS service configuration (OpenAI-compatible /v1/audio/speech)."""
+
+    model_config = SettingsConfigDict(env_prefix="TTS_")
+
+    base_url: str = "http://localhost:8000"
+    model: str = "speaches-ai/Kokoro-82M-v1.0-ONNX"
+    voice: str = "af_heart"
+    api_key: str = ""
+    timeout: float = 30.0
+    sample_rate: int = 16000
+
+
+class ReceptionistSettings(BaseSettings):
+    """AI Receptionist behavior settings."""
+
+    model_config = SettingsConfigDict(env_prefix="RECEPTIONIST_")
+
+    enabled: bool = True
+    greeting_template: str = (
+        "Hi, you've reached Robert's line. Who's calling, and what's this about?"
+    )
+    message_prompt: str = "Please leave your message after the tone."
+    listen_timeout_s: float = 15.0
+    end_of_utterance_silence_s: float = 1.2
+    message_max_seconds: int = 90
+    llm_persona: str = (
+        "You are a helpful, concise phone receptionist. Decide whether to ring "
+        "the owner, take a message, or politely decline."
+    )
+
+
 class Settings(BaseSettings):
     """Root application settings."""
 
@@ -104,6 +136,8 @@ class Settings(BaseSettings):
     classifier: ClassifierSettings = Field(default_factory=ClassifierSettings)
     llm: LLMSettings = Field(default_factory=LLMSettings)
     hold_slayer: HoldSlayerSettings = Field(default_factory=HoldSlayerSettings)
+    tts: TTSSettings = Field(default_factory=TTSSettings)
+    receptionist: ReceptionistSettings = Field(default_factory=ReceptionistSettings)
 
 
 # Singleton