move overviews to index pages

[alexandratran]

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Describe the change

Rename overview pages as index pages, update navigation and homepage accordingly, and additional minor edits across the index pages.

Fix left padding issues raised by lint codebase.

Issue fixed

fixes #200

Impacted parts

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• Documentation content
• Documentation page organization

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• Build and QA tools (e.g., lint)
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• MkDocs configuration
• Python dependencies
• Node dependencies and JavaScript
• GitHub integration

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[NicolasMassart]

just redirects, otherwise it's fine for me.

[rolandtyler]

lgtm