feat(manager): warn when closing or leaving with unsaved changes (Resources, Elements, Files)

[Ibochkarev]

What does it do?

• Unified beforeunload: In MODx.FormPanel.onReady, when confirm_navigation is on, sets window.onbeforeunload to return the unsaved-changes message only when this.isDirty(), so the warning triggers on any form change (no field blur required). Removes the duplicate handler from the resource panel that relied on warnUnsavedChanges.
• Left sidebar tab switch: When switching between Resources / Elements / Files, if any content form (resource, chunk, snippet, template, plugin, tv, file edit/create) is dirty, shows a confirm dialog; on "Yes" the tab switch proceeds, on "No" it is cancelled. Uses a new hasDirtyContentForm() helper on the layout.
• Cancel button: In the toolbar handleClick path for URL redirect (e.g. Cancel), checks the page form panel for isDirty() and shows the same confirm before calling MODx.loadPage, so Elements and Files get the same behavior as Resources.

Why is it needed?

Closing or leaving a changed resource sometimes showed a warning only when the field had lost focus, and the warning did not apply to Elements or Files. This makes the behaviour consistent: any unsaved change triggers a warning when leaving (browser close/refresh), switching the left tab, or clicking Cancel, for Resources, Elements, and Files.

How to test

1. Resources: Edit a resource (e.g. change title without blurring). Refresh or close the tab → warning. Switch left tab to Elements/Files → confirm. Click Cancel → confirm (existing). Save or Cancel+Yes → no warning.
2. Elements (Chunk/Snippet/Template/Plugin/TV): Edit an element, then refresh/close tab, switch left tab, or click Cancel → confirm when dirty; no warning after save or Cancel+Yes.
3. Files: Same for file create/edit.
4. Ensure system setting "Confirm Navigation with unsaved changes" is enabled where the feature is expected.

Related issue(s)/PR(s)

Resolves #16277

[smg6511]

@Ibochkarev - I'll take a look at this soon. A couple things:

• I removed you as an Assignee since this is your PR
• Only use const and let for variable definitions; the global var is almost never appropriate these days. It'll help if you run a javascript linter, as we have a bunch of rules set up that'll catch things like this.

[Ibochkarev]

@Ibochkarev - I'll take a look at this soon. A couple things:

• I removed you as an Assignee since this is your PR
• Only use const and let for variable definitions; the global var is almost never appropriate these days. It'll help if you run a javascript linter, as we have a bunch of rules set up that'll catch things like this.

Done — replaced var with const/let in the PR-touched code and used === for the trash tab id.