Add text_aggregation_mode parameter to TTSService

Move the sentence vs token aggregation concern into text aggregators
so all text flows through them regardless of mode. This enables
pattern detection and tag handling to work in TOKEN mode.

- Add TextAggregationMode enum (SENTENCE, TOKEN) as the user-facing
  TTS setting, separate from the internal AggregationType
- Add TOKEN mode support to Simple, SkipTags, and PatternPair aggregators
- Add text_aggregation_mode parameter to TTSService and all TTS subclasses
- Deprecate aggregate_sentences in favor of text_aggregation_mode
- Merge TTSService._process_text_frame() into a single codepath

tests/test_simple_text_aggregator.py

@@ -181,5 +181,39 @@ class TestSimpleTextAggregator(unittest.IsolatedAsyncioTestCase):
         assert result.text == "こんにちは。"
 
 
+class TestSimpleTextAggregatorTokenMode(unittest.IsolatedAsyncioTestCase):
+    def setUp(self):
+        from pipecat.utils.text.base_text_aggregator import AggregationType
+
+        self.aggregator = SimpleTextAggregator(aggregation_type=AggregationType.TOKEN)
+
+    async def test_token_passthrough(self):
+        """TOKEN mode yields text immediately without buffering."""
+        results = [agg async for agg in self.aggregator.aggregate("Hello")]
+        assert len(results) == 1
+        assert results[0].text == "Hello"
+        assert results[0].type == "token"
+
+    async def test_token_multiple_calls(self):
+        """Each aggregate call yields its text independently."""
+        r1 = [agg async for agg in self.aggregator.aggregate("Hello ")]
+        r2 = [agg async for agg in self.aggregator.aggregate("world.")]
+        assert len(r1) == 1
+        assert r1[0].text == "Hello "
+        assert len(r2) == 1
+        assert r2[0].text == "world."
+
+    async def test_token_empty_text(self):
+        """Empty text yields nothing."""
+        results = [agg async for agg in self.aggregator.aggregate("")]
+        assert len(results) == 0
+
+    async def test_token_flush_returns_none(self):
+        """Flush returns None in TOKEN mode since nothing is buffered."""
+        await self.aggregator.aggregate("Hello").__anext__()
+        result = await self.aggregator.flush()
+        assert result is None
+
+
 if __name__ == "__main__":
     unittest.main()