Document EDFA max-power characterisation; restore safe pump clamp

Swept pump-1 to find real output: 1 W (30.1 dBm) at 4000 mA, 1.22 W at
4500 mA still unsaturated. External Thorlabs meter read 1.05 W vs 1.22 W
internal PD -> telemetry is ~0.5-0.6 dB optimistic, path-dependent; treat
amp/output*_power_dbm as indicative, not calibrated.

- README: full pump-vs-output table, PD-vs-meter calibration note, >1 W
  output-connector warning, ramp/overshoot guidance
- config.h: PUMP_CURRENT_MAX_MA back to 4000 mA (1 W rating) after the
  supervised over-rating sweep; added get_thresholds probe to agiltron driver

include/config.h

@@ -26,7 +26,10 @@
 // HA number sliders are capped here. The hardware allows 8000 mA pump, but
 // the lab notes report ~2500 mA pump-1 -> ~27 dBm (~515 mW). Keep a margin.
 #define SEED_CURRENT_MAX_MA   300     // CTL200 ilmax default is 1000; seed DFB is low-power
-#define PUMP_CURRENT_MAX_MA   3000    // firmware clamps amp pump-1 to this
+// Pump-1 clamp = the 1 W rated operating point (~4000 mA, measured 2026-06-17).
+// Raise deliberately only for supervised over-rating characterisation; it is a
+// guardrail against accidental over-drive, not a safety interlock.
+#define PUMP_CURRENT_MAX_MA   4000
 
 // ── Serial links to the instruments (wired in later increments) ─────
 // UART0 stays the USB console. The classic ESP32 has 3 hardware UARTs.