Refactor var to const/let in core JS utilities (1/4)

[limad]

Summary

First of four migration PRs splitting the var → const/let work from #3297 by functional domain. This batch covers 11 utility/AJAX-boilerplate files:

jeedom.class.js   private.class.js   core.js
cache.class.js    queue.class.js     listener.class.js
network.class.js  security.class.js  message.class.js
dataStore.class.js  repo.class.js

Most of these files follow the same uniform AJAX boilerplate pattern (paramsRequired, paramsSpecifics, try/catch, domUtils.ajax(paramsAJAX)), so the migration is largely mechanical: var X = ... → const X = ... for declarations that are never reassigned, let for the rest.

Incidental fixes (caught during migration)

• jeedom.class.js — removed the top-level var Highcharts declaration. With var at top-level it became window.Highcharts and was overwritten by highstock.js loaded later. With const/let it would shadow window.Highcharts, leaving the local binding undefined and crashing jeedom.init() with TypeError: Highcharts.setOptions is undefined. Fix: rely on window.Highcharts directly.
• private.class.js — renamed top-level var init to _init. With const init it collided with the global function init() declared in core.js (SyntaxError: redeclaration of non-configurable global property init).
• private.class.js — const value → let value (was reassigned by value += '', would have thrown TypeError: Assignment to constant variable).
• private.class.js — removed unused var param = null (dead code).

Test plan

• Reload any Jeedom page — verify jeedom.init() runs without console errors
• Open a chart that uses Highcharts (history, dashboard widget) — verify it renders
• Trigger any API call going through jeedom.private.getParamsAJAX — verify the result handler still works
• Verify init() and _init() both work where used

Part of the split following #3297 discussion. Stacks logically with #3299 (ESLint baseline) but does not depend on it.

[kwizer15]

I noticed the space after = got stripped on empty initializations: const paramsRequired =[] instead of const paramsRequired = []. It's inconsistent with the other assignments in the diff (const params = domUtils.extend(...) keeps the space) and breaks space-infix-ops.

[limad]

Good catch @kwizer15, thanks. Fixed in 148493b — restored the space after = on the 68 affected lines in jeedom.class.js. The same artefact appeared in cmd.class.js (PR #3301) and is fixed there in 5e57ff9. The other migration PRs (#3302, #3303) and the desktop/js work were not affected — verified with grep -rE "(const|let)\s+\w+\s*=[\[\{]" after the fix.