Fix GuiTest.json: was neither small nor fast

Two compounding problems, found by actually running it:
- pot_mass=1/water_mass=1 (~2kg) is far lighter than the mass the real
  PID gains are tuned for (~30kg, matching the real recipes) - same
  heater power swings a 2kg pot far faster than the gains expect,
  causing massive overshoot (24 -> 37.5 instead of holding at 24).
  Fixed by using the same realistic mass as sud_0010.json/sud_0020.json.
- The overshoot then needed a passive cooldown back down to the next
  step's target - independent of any declared rate, governed by the
  plant's L/C time constant (~350 min here), regardless of mass.
  Removed the (now unnecessary, since the overshoot is gone) explicit
  cooldown step too.

Predicted/actual duration drops from ~408 min to ~18-21 min - verified
both via components/sud_forecast.py's estimator and a live run against
the real server (reaches DONE, no controller chattering).

sude/GuiTest.json

@@ -1,15 +1,15 @@
 {
 	"Name": "GuiTest",
 	"Description": "Small, fast schedule for exercising the GUI (load/start/pause/stop/restart) without waiting through a real brew",
-	"pot_mass": 1,
+	"pot_mass": 5.96,
 	"pot_material": "Edelstahl 18/10",
 	"default": {
 		"step": {
 			"descr": "Put description here",
 			"user_message": "Put user message here",
 			"user_wait_for_continue": false,
-			"grain_mass": 0,
-			"water_mass": 1,
+			"grain_mass": 5.21,
+			"water_mass": 22,
 			"temperature": 0,
 			"ramp": {
 				"rate": 5.0,
@@ -61,16 +61,6 @@
 				"duration": 1
 			}
 		},
-		{
-			"descr": "Cool back to 22",
-			"temperature": 22,
-			"ramp": {
-				"rate": 5.0
-			},
-			"hold": {
-				"duration": 1
-			}
-		},
 		{
 			"descr": "Final confirm",
 			"user_message": "Quittieren zum Abschluss",