WYSIWYG field renders collapsed (150px) when it is the only field in a content type tab

Problem Statement

When a WYSIWYG (TinyMCE) field is the only field on a tab of a content type, the editor's inner editable iframe falls back to TinyMCE's default height (~150px) instead of expanding to fill its container. Existing content is visually truncated mid-paragraph and scrolls inside a small window, with a large dead-whitespace area below the editor.

Content is not lost — it's intact in code view and via API. This is display-only, but it significantly degrades the editing experience for content teams.

Steps to Reproduce

1. Create a content type with fields on the first tab (e.g. Title, Description)
2. Add a second tab (tab divider) containing only one WYSIWYG field
3. Create a contentlet, add several paragraphs of text to the WYSIWYG, and Save
4. → Editor immediately re-renders collapsed (~150px) with whitespace below
5. Close and reopen the contentlet (opens on first tab), switch to the WYSIWYG tab
6. → Editor renders collapsed again

https://drive.google.com/file/d/13hiQ6PhJ-_unA3Wx4liPVd7cAeRcHv7S/view?usp=drive_link

Acceptance Criteria

Expected Behavior
The WYSIWYG editable area expands to fill its container (~587px in the repro) regardless of whether it is the only field on the tab, matching the behavior when other fields share the tab.

Actual Behavior
Inner editable iframe stays at the 150px TinyMCE default; content clips and scrolls within it; remainder of the container renders as empty whitespace.

dotCMS Version

26.07.06-02

Severity

Medium - Some functionality impacted

Links

https://helpdesk.dotcms.com/a/tickets/38359

Reproduce the collapsed WYSIWYG behavior using a content type with a second tab containing only one WYSIWYG field, then compare it with a tab where other fields are present. Confirm that the editable area expands to fill the container and that existing content no longer clips or scrolls inside a 150px area.