Fix accordion gap token overrides

[Aurantium-47]

Description

• Set the default accordion gap in $accordion-tokens.
• Remove the .accordion-gap declaration that replaces a custom token value.
• Update the gap documentation after removing that declaration.
• Validation: all npm test stages pass when run serially, including 1,357 browser tests and coverage gates. npm run css-test passes 48 specs.
• A compiled Sass/Chromium check confirms custom gaps of 3rem and 0. Default spacing, inline overrides, and ordinary accordions stay unchanged.

Motivation & Context

An accordion configured with --accordion-gap: 3rem still renders the default gap. The modifier overrides the configured token. This change preserves the default appearance and lets the Sass configuration take effect.

AI assistance: Codex prepared the patch and validation.

Type of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Refactoring (non-breaking change)
• Breaking change (fix or feature that would change existing functionality)

Checklist

• I have read the contributing guidelines
• My code follows the code style of the project (using npm run lint)
• My change introduces changes to the documentation
• I have updated the documentation accordingly
• I have added tests to cover my changes
• All new and existing tests passed

Live previews

Accordion gap documentation preview

Related issues

Fixes #43049.