Butterfly EDFA Rack bridge: seed + EDFA over WiFi/MQTT to Home Assistant

ESP32 firmware bridging the 1550 nm MOPA (Koheron CTL200 seed + Agiltron
M511 two-stage EDFA) to MQTT/HA as a single device. Telemetry and control
for both instruments verified end-to-end: MQTT command -> seed lasing ->
booster ramp to 27 dBm (~515 mW) at the documented 2500 mA operating point.

- PlatformIO/Arduino project, project-local venv, Makefile upload flow
- Koheron ASCII driver on UART2; Agiltron binary 0x55AA driver on UART1
- HA discovery (sensors, binary_sensors, switches, numbers); LWT availability
- Static IP, firmware current clamps on seed and booster pump

include/secrets.example.h

@@ -0,0 +1,15 @@
+// Copy to secrets.h and fill in. secrets.h is git-ignored.
+#pragma once
+
+#define WIFI_SSID      "your-ssid"
+#define WIFI_PASSWORD  "your-password"
+
+#define MQTT_BROKER    "192.168.0.102"   // HA / mosquitto host
+#define MQTT_PORT      1883
+// Broker allows anonymous; leave user/pass empty unless that changes.
+#define MQTT_USER      ""
+#define MQTT_PASSWORD  ""
+
+// Logical unit slug -> topics live under lab/laser/<DEVICE_NAME>/...
+#define DEVICE_NAME    "butterfly_edfa_rack"
+#define DEVICE_FRIENDLY "Butterfly EDFA Rack"