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>

espnow-sender/src/peer_table.py

@@ -0,0 +1,43 @@
+"""LRU table of ESP-NOW peer MACs seen on uplink."""
+
+from espnow_wire import BROADCAST_MAC
+
+try:
+    from settings import Settings
+except ImportError:
+    Settings = None
+
+
+class PeerTable:
+    def __init__(self, max_peers=20):
+        self._max = max(1, int(max_peers))
+        self._order = []
+        self._names = {}
+
+    def touch(self, mac_bytes, name=None):
+        if not mac_bytes or len(mac_bytes) != 6:
+            return
+        if mac_bytes in self._order:
+            self._order.remove(mac_bytes)
+        elif len(self._order) >= self._max:
+            old = self._order.pop(0)
+            self._names.pop(old, None)
+        self._order.append(mac_bytes)
+        if name:
+            self._names[mac_bytes] = str(name)
+
+    def peers(self):
+        return list(self._order)
+
+    def is_broadcast_mac(self, mac_bytes):
+        return mac_bytes == BROADCAST_MAC
+
+
+def load_max_peers():
+    if Settings is None:
+        return 20
+    try:
+        s = Settings()
+        return int(s.get("max_peers", 20))
+    except Exception:
+        return 20