refactor: adopt POSITIONS constants and fix ESLint warnings

Replace hardcoded position strings with POSITIONS.* constants.
Prefix unused variables with _ to resolve no-unused-vars warnings.
Fix no-prototype-builtins where applicable.

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

additional_nodes/recirculation-pump.js

@@ -3,7 +3,6 @@ module.exports = function(RED) {
         RED.nodes.createNode(this, config);
         var node = this;
 
-        let name = config.name;
         let F2 = parseFloat(config.F2);
         const inlet_F2 = parseInt(config.inlet);
 

additional_nodes/settling-basin.js

@@ -3,7 +3,6 @@ module.exports = function(RED) {
         RED.nodes.createNode(this, config);
         var node = this;
 
-        let name = config.name;
         let TS_set = parseFloat(config.TS_set);
         const inlet_sludge = parseInt(config.inlet);