Website navigation improvements - v1

[lihter]

• content on the homepage directly
• homepage has left sidebar
• other OWASP Initiatives are linked within text
• navigator and security matrix images are on the homepage

[github-actions[bot]]

Visit the preview URL for this PR (updated for commit a9081e8):

https://owasp-ai-exchange--pr37-website-navigation-i-a977pfuw.web.app

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