chore(02-03): replace python-mpv with librosa>=0.10.0 in pyproject.toml

- Remove python-mpv>=1.0.5 (server-side playback replaced by browser audio)
- Add librosa>=0.10.0 for beat detection and tempo analysis
- Keep soundfile, numpy, python-multipart (still needed)

pyproject.toml

@@ -13,9 +13,9 @@ dependencies = [
     "aiofiles>=24.0.0",
     "python-dotenv>=1.0.0",
     "structlog>=24.0.0",
-    "python-mpv>=1.0.5",
     "soundfile>=0.12.0",
     "numpy>=1.26.0",
+    "librosa>=0.10.0",
     "python-multipart>=0.0.9",
 ]