fix: expand doc main container to full width on mobiles

[lex111]

Motivation

In #7025 I forgot to check the doc layout for mobiles, which resulted in horizontal scrolling on small screens.

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✅ [V2]

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[github-actions]

⚡️ Lighthouse report for the changes in this PR:

Category	Score
🟠 Performance	52
🟢 Accessibility	100
🟢 Best practices	92
🟢 SEO	100
🟢 PWA	90

Lighthouse ran on https://deploy-preview-7030--docusaurus-2.netlify.app/

[github-actions]

Size Change: +23 B (0%)

Total Size: 806 kB

ℹ️ View Unchanged

Filename	Size	Change
website/.docusaurus/globalData.json	49.9 kB	0 B
website/build/assets/css/styles.********.css	105 kB	+23 B (0%)
website/build/assets/js/main.********.js	613 kB	0 B
website/build/index.html	38.4 kB	0 B

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