ui: show water level and status line before any sud is loaded

Pot config (water_mass, volumen) sent in System message at startup.
app.js stores potConfig and uses it in updatePotVisualization/
updateStatusLine when sudEmpty, showing startup fill level and
"No schedule – N L water" without requiring a sud to be loaded first.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

config-sim.json.tpl

@@ -47,6 +47,8 @@
 		"mass": 5.96,
 		"material": "Edelstahl 18/10",
 		"L": 0.2,
-		"Td": 17
+		"Td": 17,
+		"water_mass": 22,
+		"volumen": 30
 	}
 }