Full rearchitecture using Claude

- event bus systen
- all components are independent
- preparation for web frontend

python-backend/musicmouse/devices/transport.py

@@ -0,0 +1,21 @@
+"""The seam between :class:`~musicmouse.devices.mouse.MusicMouseDevice` and the wire.
+
+Kept free of any serial import so the simulator can substitute a transport without
+pulling in ``pyserial-asyncio``.
+"""
+
+from __future__ import annotations
+
+from typing import Protocol
+
+__all__ = ["Transport"]
+
+
+class Transport(Protocol):
+    def write(self, data: bytes) -> None:
+        """Send bytes to the firmware. Dropping them while disconnected is fine:
+        the device re-applies its memorized state once the link is back."""
+        ...
+
+    @property
+    def connected(self) -> bool: ...