Update ifo logo, fix citation

[mjbloemer]

This PR updates the ifo logo and fixes a typo in the citation file.

[Copilot]

Pull Request Overview

This PR updates branding elements and corrects a typographical error in the project citation. The changes focus on maintaining consistency in the project's visual identity and ensuring accuracy in academic references.

• Updated ifo logo for consistent branding
• Fixed capitalization error in the citation title

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[read-the-docs-community]

Documentation build overview

📚 gettsim | 🛠️ Build #29938398 | 📁 Comparing b244bea against latest (2b65506)

🔍 Preview build

Show files changed (2 files in total): 📝 2 modified | ➕ 0 added | ➖ 0 deleted

File	Status
how_to_guides/modifications_of_policy_environments.html	📝 modified
tutorials/visualizing_the_system.html	📝 modified

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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