Feature: ESP-NOW auto mesh + Nodes (ESP-NOW) UI

- Broadcast beacons with magic KLNK; no MAC pairing
- Track up to 8 peer MACs; stale after 12s
- Telemetry/health JSON: espnow_ok, espnow_peers
- Web metric + OLED health line
- README: ESP-NOW section and channel requirement

Made-with: Cursor

README.md

@@ -237,7 +237,7 @@ Connect to the WiFi access point, then open the control panel in a browser.
         Temperature (Celsius)
         Free heap (KB)
 
-    [METRICS GRID - 12 stats updated every 1 second]
+    [METRICS GRID - stats updated every 1 second]
 
     Effective TX power (dBm)
     Radio 1 status
@@ -249,6 +249,7 @@ Connect to the WiFi access point, then open the control panel in a browser.
     Hop count Radio 2 (total since boot)
     Combined hops per second
     WiFi clients on AP
+    Nodes (ESP-NOW): count of other boards running this firmware in range
     Uptime
     24-hour mission progress bar in the header
 
@@ -262,6 +263,32 @@ Connect to the WiFi access point, then open the control panel in a browser.
 
 ---
 
+## ESP-NOW NODE MESH
+
+    Multiple boards running the same firmware discover each other automatically
+    over ESP-NOW. No MAC address entry and no pairing step.
+
+    How it works:
+        Each unit broadcasts a small beacon every 750 ms to the ESP-NOW
+        broadcast address. The payload starts with a fixed magic signature
+        so only this firmware is counted.
+        When a unit hears a valid beacon, it records the sender MAC and
+        refreshes a last-seen time. The web UI metric "Nodes (ESP-NOW)" is
+        the number of other units heard within the last 12 seconds.
+        The OLED health page shows the same count after "ESPNOW".
+
+    Requirements for links to work:
+        All units must share the same Wi-Fi radio channel as the soft-AP.
+        This build starts the AP on channel 1. Do not run different channel
+        settings on different boards unless you change the code consistently.
+        Range is typical 2.4 GHz ESP-NOW range (often tens of meters indoors,
+        more line-of-sight).
+
+    Note: This release only counts peers and logs new MACs. It does not yet
+    sync jamming state or share telemetry over ESP-NOW.
+
+---
+
 ## RELIABILITY FEATURES (24-HOUR OPERATION)
 
 The system is designed to run unattended at full power indefinitely.