TextFrame: add skip_tts field

This lets a text frame bypass TTS while still being included in the LLM
context. Useful for cases like structured text that isn’t meant to be spoken but
should still contribute to context.

src/pipecat/frames/frames.py

@@ -305,6 +305,11 @@ class TextFrame(DataFrame):
     """
 
     text: str
+    skip_tts: bool = field(init=False)
+
+    def __post_init__(self):
+        super().__post_init__()
+        self.skip_tts = False
 
     def __str__(self):
         pts = format_pts(self.pts)