Refactor project structure and enhance backend integration

- Expanded package inclusion in `pyproject.toml` to support new modules.
- Introduced new `adapters` and `protocol` packages for better organization.
- Added backend adapter implementations for control plane integration.
- Updated main application imports to reflect new package structure.
- Removed deprecated core components and adjusted documentation accordingly.
- Enhanced architecture documentation to clarify the new runtime and integration layers.

engine/runtime/pipeline/tts_flow.py

@@ -0,0 +1,15 @@
+"""TTS flow helpers extracted from the duplex pipeline.
+
+This module is intentionally lightweight for phase-wise migration.
+"""
+
+from __future__ import annotations
+
+from providers.common.base import TTSChunk
+
+
+def chunk_duration_ms(chunk: TTSChunk) -> float:
+    """Estimate chunk duration in milliseconds for pcm16 mono."""
+    if chunk.sample_rate <= 0:
+        return 0.0
+    return (len(chunk.audio) / 2.0 / float(chunk.sample_rate)) * 1000.0