feat: implement volume boost functionality with signal-based multiplier and audio processing override

tests/test_api_surface.py

@@ -20,6 +20,7 @@ EXPECTED_ENDPOINTS = {
     ("post", "/api/skip"),
     ("post", "/api/stop"),
     ("post", "/api/volume"),
+    ("post", "/api/volume_boost"),
     ("post", "/api/loop"),
     ("post", "/api/loop_playlist"),
     ("post", "/api/loop_cycle"),