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>

src/configs/settler.json

@@ -0,0 +1,75 @@
+{
+    "general": {
+      "name": {
+        "default": "Settler",
+        "rules": {
+          "type": "string",
+          "description": "A human-readable name for this settler."
+        }
+      },
+      "id": {
+        "default": null,
+        "rules": {
+          "type": "string",
+          "nullable": true,
+          "description": "Unique identifier for this settler node."
+        }
+      },
+      "unit": {
+        "default": null,
+        "rules": {
+          "type": "string",
+          "nullable": true,
+          "description": "Default measurement unit."
+        }
+      },
+      "logging": {
+        "logLevel": {
+          "default": "info",
+          "rules": {
+            "type": "enum",
+            "values": [
+              { "value": "debug", "description": "Verbose diagnostic messages." },
+              { "value": "info", "description": "General informational messages." },
+              { "value": "warn", "description": "Warning messages." },
+              { "value": "error", "description": "Error level messages only." }
+            ]
+          }
+        },
+        "enabled": {
+          "default": true,
+          "rules": {
+            "type": "boolean",
+            "description": "Enable or disable logging."
+          }
+        }
+      }
+    },
+    "functionality": {
+      "softwareType": {
+        "default": "settler",
+        "rules": {
+          "type": "string",
+          "description": "Software type identifier for parent-child registration."
+        }
+      },
+      "role": {
+        "default": "Secondary settler for sludge separation",
+        "rules": {
+          "type": "string",
+          "description": "Describes the functional role of this node."
+        }
+      },
+      "positionVsParent": {
+        "default": "downstream",
+        "rules": {
+          "type": "enum",
+          "values": [
+            { "value": "upstream", "description": "Upstream of parent equipment." },
+            { "value": "atEquipment", "description": "At equipment level." },
+            { "value": "downstream", "description": "Downstream of parent equipment." }
+          ]
+        }
+      }
+    }
+  }