Fix: HTML tags are not working in Background Video [ED-25625] - #37407

## PR Checklist
- [x] The commit message follows our guidelines:
https://github.com/elementor/elementor/blob/master/.github/CONTRIBUTING.md

## PR Type
- [x] Bugfix

## Summary

This PR can be summarized in the following changelog entry:

* Fix: HTML tags do not work in Background Video

## Description

* The Background Video template hardcoded `<div>` and `e-default-div`,
ignoring the computed `tag` from the HTML Tag setting. It now renders
`{{ tag | e('html_tag') }}` and `m.default_tag_class(tag)`, same as
Flexbox.
* Added `main` and `nav` to the `tag` enum, its description, and the
HTML Tag control options (matching Flexbox).

## Test instructions

* Add a Background Video element, set Settings > HTML Tag to Section (or
Main / Nav).
* The editor preview and the published page render `<section class="...
e-default-section">`; playback and play/pause controls keep working.
* An element without an explicit tag still renders as `<div>`.

## Quality assurance

- [x] I have tested this code to the best of my abilities
- [x] I have added unittests to verify the code works as intended

PHPUnit: schema enum, render per tag (8 tags), default div, invalid tag
fallback. Playwright: tag applied in editor and frontend, Main/Nav
options present.

Fixes #37393

Jira: [ED-25625](https://elementor.atlassian.net/browse/ED-25625)

[ED-25625]:
https://elementor.atlassian.net/browse/ED-25625?atlOrigin=eyJpIjoiNWRkNTljNzYxNjVmNDY3MDlhMDU5Y2ZhYzA5YTRkZjUiLCJwIjoiZ2l0aHViLWNvbS1KU1cifQ
## Visual proof

**Broken:** Changing HTML Tag on Background Video had no effect; the
canvas and published page always rendered a div wrapper.
**Where:** Edit with Elementor → select Background Video → Settings →
HTML Tag
**Steps:** Add Background Video → select it → open Settings → set HTML
Tag to Section → view the element on the canvas
**Pass:** The canvas wrapper is a section and Background Video still
plays with visible controls
**Fail:** The canvas wrapper stays a div no matter which HTML Tag is
selected


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Co-authored-by: Cursor <cursoragent@cursor.com>

…g in Background Video [ED-25625] (#37412)

Automatic cherry-pick of
[#37407](#37407) to
`release/stable` branch.

      **Source:** elementor/elementor
      **Original Author:** @max-zu
      **Trigger:** Label `cp_release/stable` added to closed PR

---------

Co-authored-by: Maksim Zubov <zubovmaksim@gmail.com>
Co-authored-by: Cursor <cursoragent@cursor.com>
Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>