feat(espnow): broadcast delivery with group-filtered routing

Send presets and select on broadcast with groups; unicast only for
per-device settings. V1 select as [preset_id, step?]. Sequence steps
use beat counts; manual presets get select each beat, auto only on
step change. Bridge downlink router, Pi envelope delivery, and tests.

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

src/settings.py

@@ -51,7 +51,7 @@ class Settings(dict):
             self.save()
         # ESP-NOW STA channel (2.4 GHz) for LED drivers / bridge alignment; 1–11
         if 'wifi_channel' not in self:
-            self['wifi_channel'] = 6
+            self['wifi_channel'] = 1
         # WebSocket URL of ESP-NOW bridge (Pi is client), e.g. ws://192.168.4.1/ws
         if 'bridge_ws_url' not in self:
             self['bridge_ws_url'] = ''