Add position constants, reactor/settler config schemas

- New src/constants/positions.js: POSITIONS enum (upstream/downstream/atEquipment/delta)
- New src/configs/reactor.json: Full schema for CSTR/PFR reactor parameters and ASM3 initial state
- New src/configs/settler.json: Schema for settler node
- Export POSITIONS, POSITION_VALUES, isValidPosition from index.js

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

index.js

@@ -26,6 +26,7 @@ const predict = require('./src/predict/predict_class.js');
 const interpolation = require('./src/predict/interpolation.js');
 const childRegistrationUtils = require('./src/helper/childRegistrationUtils.js');
 const { loadCurve } = require('./datasets/assetData/curves/index.js');
+const { POSITIONS, POSITION_VALUES, isValidPosition } = require('./src/constants/positions.js');
 const Fysics = require('./src/convert/fysics.js');
 
 // Gravity helper (used by rotatingMachine for efficiency calculations)
@@ -52,5 +53,8 @@ module.exports = {
     MenuManager,
     childRegistrationUtils,
     loadCurve,
-    gravity
+    gravity,
+    POSITIONS,
+    POSITION_VALUES,
+    isValidPosition
 };