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>

tests/models/test_device.py

@@ -150,6 +150,27 @@ def test_device_duplicate_names_allowed():
     assert devices.read(a1)["name"] == devices.read(a2)["name"] == "alpha"
 
 
+def test_upsert_espnow_announced():
+    devices = _fresh_device()
+    m = "e8f60a16dad0"
+    i1, p1 = devices.upsert_espnow_announced(
+        m,
+        "led-test",
+        num_leds=120,
+        color_order="grb",
+        startup_mode="last",
+        brightness=70,
+    )
+    assert i1 == m and p1 is True
+    d = devices.read(m)
+    assert d["transport"] == "espnow"
+    assert d["address"] == m
+    assert d["name"] == "led-test"
+    assert d["num_leds"] == 120
+    i2, p2 = devices.upsert_espnow_announced(m, "led-test")
+    assert i2 == m and p2 is False
+
+
 def test_device_duplicate_mac_rejected():
     devices = _fresh_device()
     devices.create("one", address="aa:bb:cc:dd:ee:ff")
@@ -163,6 +184,7 @@ def test_device_duplicate_mac_rejected():
 if __name__ == "__main__":
     test_device()
     test_upsert_wifi_tcp_client()
+    test_upsert_espnow_announced()
     test_device_can_change_address()
     test_device_duplicate_names_allowed()
     test_device_duplicate_mac_rejected()