feat: auto-disable message authentication at startup

SNEK resets to authentication=enabled on every restart and does not persist
the state anywhere. The entrypoint now waits for the SNEK API to be ready
and POSTs to /ned/saturation to disable auth automatically.

- Registered devices without HMAC public keys (e.g. demo Sens'it) are
  decoded immediately on first boot and after any pod restart
- To re-enable auth in production, comment the polling block in entrypoint.sh

README updated with details in the "Configuration des devices" section.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

build/entrypoint.sh

@@ -16,5 +16,23 @@ cd /opt/snek
 ./foxctl || echo "foxctl RC=$? (may be normal if firmware already loaded)"
 sleep 2
 
+# Auto-disable message authentication after SNEK is up
+# SNEK resets to auth=enabled on every restart; we disable it so registered
+# devices without a public key can still be decoded
+(
+    for i in $(seq 1 30); do
+        if curl -sf http://localhost:8085/ned/saturation > /dev/null 2>&1; then
+            echo "==> SNEK API ready, disabling message authentication..."
+            curl -sX POST -H "Content-Type: application/json" \
+                -d '{"saturation":false,"authentication":false,"dongleDisconnected":false}' \
+                http://localhost:8085/ned/saturation > /dev/null
+            echo "==> Message authentication disabled"
+            exit 0
+        fi
+        sleep 2
+    done
+    echo "!!! Warning: SNEK API not reachable after 60s, auth not toggled"
+) &
+
 echo "==> Starting SNEK main_sigfox on port 8085..."
 exec ./main_sigfox