Refactor var to const/let in UI rendering files (3/4)

[limad]

Summary

Third of four migration PRs splitting #3297 by functional domain. This batch covers 7 files handling UI rendering (views, plans, timeline, history charts, widgets, plugin templates):

view.class.js    plan.class.js     plan3d.class.js
timeline.class.js   history.class.js     widgets.class.js
plugin.template.js

Incidental fixes (caught during migration)

• history.class.js — var series was declared in two mutually-exclusive if/else blocks (if (data.result.timelineOnly) { var series = {...} } else { var series = {...} }) but referenced in code located after the block (in addSeries(series) calls, in chart config object, etc.). With var, function-scoped hoisting unified the two declarations and made the reference work. Migrated to const/let, it became block-scoped and threw ReferenceError: series is not defined. Fix: hoisted to a single let series declared before the if/else, with assignments in each branch.
• plugin.template.js — const eqLogic at line 300 was reassigned at line 311 by eqLogic = saveEqLogic(eqLogic). Changed to let eqLogic to avoid TypeError: Assignment to constant variable on equipment save flow.

Test plan

• Open the History page and select a command — verify charts render
• Toggle the History 'compare' mode — verify both series render correctly (this is the path that exercises the series hoist fix)
• Open a View page that contains a graph zone — verify rendering and data-option attributes are populated
• Open a 2D Plan and a 3D Plan if you have them — verify display
• Open the Timeline page — verify timeline renders
• Open a plugin equipment, modify a setting, click 'Sauvegarder' — verify save flow (this is the path that exercises the eqLogic const→let fix)

Part of the split following #3297 discussion.