fix: validation added to fix a11y issue

[jesusbalderramawgu]

Description

PR to fix an a11y issue, it closes this issue.

Issue

In summary we have currently two Skip links and we should have only one "globally"

Fix

Ensure the skip link targets the main content container using a valid anchor or focusable element at the start of the primary content region.

Testing instructions

Given you open a unit in the learning MFE at http:///learning/course/<course_id>/<sequence_id>/<unit_id>
When you press Tab from the address bar
Then

The first focusable element is the top-level "Skip to main content" link (from the MFE header).
Subsequent Tab presses go through the MFE header links and directly into the first control inside the unit iframe.
No second "Skip to main content" link appears between the header and the unit content.
DOM check: In DevTools, inspect iframe.unit-iframe > body. There must be no element.

Screenshots

Before the fix

After the fix

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[Copilot]

🟢 Approval recommended

The change is small, localized, and consistent with the stated a11y goal, with only a minor maintainability nit noted.

Pull request overview

This PR adjusts LMS base template rendering to prevent an extra “Skip to main content” link from appearing in chromeless/iframe contexts (notably the Learning MFE unit iframe), aligning with the accessibility goal of having a single global skip link.

Changes:

• Conditionally renders the LMS skip link only when the LMS header is enabled.
• Prevents the skip link from appearing on pages rendered with disable_header (commonly used for embedded/chromeless views).

File summaries

File	Description
lms/templates/main.html	Wraps the LMS skip-link output in a not disable_header condition to avoid duplicate skip links in chromeless/iframe contexts.

Review details

Suppressed comments (1)

lms/templates/main.html:210

• This introduces a second separate if not disable_header block; the skip link can be placed inside the existing header guard to avoid duplicated conditionals and keep related header/chrome elements grouped together.

    % if not disable_header:
    <a class="nav-skip sr-only sr-only-focusable" href="#main">${_("Skip to main content")}</a>
    % endif

    % if not disable_header:
        <%include file="${static.get_template_path('header.html')}" args="online_help_token=online_help_token" />
        <%include file="/preview_menu.html" />
    % endif

• Files reviewed: 1/1 changed files
• Comments generated: 0
• Review effort level: Lite

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