fix: 优化架构

engine/adapters/tts/mock_adapter.py

@@ -0,0 +1,15 @@
+from __future__ import annotations
+
+from pathlib import Path
+
+from .base import BaseTTS
+
+
+class MockTTS(BaseTTS):
+    def generate(self, text: str, output_path: str | Path) -> str:
+        # No-op for offline tests: return empty path so video adapter skips audio.
+        output_path = Path(output_path)
+        output_path.parent.mkdir(parents=True, exist_ok=True)
+        output_path.write_bytes(b"")
+        return str(output_path)
+