feat(espnow): Pi bridge client, binary wire, and espnow-sender firmware

Replace serial/Wi-Fi driver transport paths with WebSocket bridge client,
binary espnow_wire delivery, device announce registry, and restructured
espnow-sender (AP + broadcast passthrough). Includes docs and tests.

Co-authored-by: Cursor <cursoragent@cursor.com>

espnow-sender/lib/microdot/__init__.py

@@ -0,0 +1,2 @@
+from microdot.microdot import Microdot, Request, Response, abort, redirect, \
+    send_file  # noqa: F401