feat(espnow): add wire transport and simplify broadcast main

Binary espnow_wire/espnow_transport modules plus a minimal main that
broadcasts a JSON hello and polls ESP-NOW while running presets.

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

src/device_groups.py

@@ -0,0 +1,16 @@
+"""In-memory group membership for GROUP_CMD filtering."""
+
+_groups = []
+
+
+def groups_replace(group_ids):
+    global _groups
+    _groups = [str(g) for g in group_ids]
+
+
+def in_group(group_id):
+    return str(group_id) in _groups
+
+
+def list_groups():
+    return list(_groups)