fix(grid): make --grid-maxWidth a true maximum instead of a fixed width

[fbasmaison-lucca]

Description

• Grid: --grid-maxWidth now acts as a true maximum, not a fixed width.
• Form grids keep an auto inline-size.
• They no longer occupy 50rem when their content is narrower.

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Note for reviewers

• A few occurrences of --grid-max-width found outside LF.
• #3154 reverted this same approach.
  • It broke horizontal fieldsets in their flex-based layout at the time.
• The fieldset now uses a CSS grid layout (grid-template-columns: 1fr auto).
  • A child grid stretches to fill its cell.
  • The old breakage should no longer apply.

Context

• mod-form sets --grid-maxWidth: var(--components-form-maxWidth, 50rem).
• The grid consumed it through inline-size.
  • max-inline-size: 100% clamped it.
  • Result: a form grid always occupied 50rem, even with narrower content.
• The default --grid-maxWidth: none is invalid for inline-size.
  • It resolved to auto only through IACVT.
  • It silently overrode any other inline-size declaration in the cascade.
• Downstream symptom example: spurious horizontal scrollbar in a dialog.
  • The form grid forced its fieldset wider than the dialog content.
  • Sidenote: screenshots below come from LuccaSA/Cleemy.Front#905.
  • That PR works around the issue on the product side with pr-u-minInlineSize0.

Before:

After:

Solution

• Apply the variable through max-inline-size instead of inline-size.
  • This matches the original intent (commented-out line).
• Remove the max-inline-size: 100% clamp.
  • Nothing can force an overflow without a fixed inline-size.
• The default none is a valid value for max-inline-size.
  • No more reliance on IACVT.
• Align the grid with the form component.
  • The form already uses max-inline-size: var(--components-form-maxWidth).

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Fixes #5188

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[github-actions]

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[Copilot]

Pull request overview

Updates grid sizing so --grid-maxWidth acts as a maximum and avoids forcing form grids beyond their container.

Changes:

• Applies --grid-maxWidth through max-inline-size.
• Removes the fixed inline size and redundant 100% clamp.

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[shajz]

@fbasmaison-lucca
Not a reviewer anymore but I notice this PR fixes my issue #5188 (inline-size: none invalid, resolved as auto by IACVT).

Might you add a tiny Fixes #5188 in the description please ? 😊

[vvalentin-lucca]

This breaks the horizontal layout of the fieldset component.

Before:

After: