Clarify that ServiceSettings and subclasses represent runtime-updatable settings

Update docstrings for ServiceSettings, LLMSettings, TTSSettings, and STTSettings to make clear these capture only the subset of service configuration that can be changed while the pipeline is running via UpdateSettingsFrame, not all constructor parameters.

src/pipecat/services/settings.py

@@ -92,7 +92,13 @@ _S = TypeVar("_S", bound="ServiceSettings")
 
 @dataclass
 class ServiceSettings:
-    """Base class for service settings.
+    """Base class for runtime-updatable service settings.
+
+    These settings represent the subset of a service's configuration that can
+    be changed **while the pipeline is running** (e.g. switching the model or
+    changing the voice).  They are *not* meant to capture every constructor
+    parameter — only those that support live updates via
+    ``UpdateSettingsFrame``.
 
     Every AI service type (LLM, TTS, STT) extends this with its own fields.
     Fields default to ``NOT_GIVEN`` so that an instance can represent either
@@ -244,7 +250,9 @@ class ServiceSettings:
 
 @dataclass
 class LLMSettings(ServiceSettings):
-    """Settings for LLM services.
+    """Runtime-updatable settings for LLM services.
+
+    See ``ServiceSettings`` for the general concept.
 
     Parameters:
         model: LLM model identifier.
@@ -279,7 +287,9 @@ class LLMSettings(ServiceSettings):
 
 @dataclass
 class TTSSettings(ServiceSettings):
-    """Settings for TTS services.
+    """Runtime-updatable settings for TTS services.
+
+    See ``ServiceSettings`` for the general concept.
 
     Parameters:
         model: TTS model identifier.
@@ -302,7 +312,9 @@ class TTSSettings(ServiceSettings):
 
 @dataclass
 class STTSettings(ServiceSettings):
-    """Settings for STT services.
+    """Runtime-updatable settings for STT services.
+
+    See ``ServiceSettings`` for the general concept.
 
     Parameters:
         model: STT model identifier.