fix: Allow closing the search via the search button

[MoritzWeber0]

Especially on mobile devices, space is limited and users may not have enough space to close the search if they want to. This PR changes the "open search" behavior to a "toggle search" behavior (open if search is closed, close if search is open).

In addition, two bugs are fixed:

• The overlay wasn't displayed when the user navigated to the search field on the home page via tab.
• The overlay wasn't closed if the search was opened via click and then moved out using the tab character (this will probably change when we implement the focus trapping, but for now it's the best solution I think).

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[github-actions]

Hi there! 👋

Thank you for your contribution to the FIP Guide! 🚀
We appreciate your effort in making rail staff travel information more accessible. 🚄

Checklist before merging:

• Added a description to the Pull Request
• Checked the License of new pictures (non-commercial use without attribution)
• Modified content in English
• Modified content in German
• Modified content in French

[therobrob]

Works nice! Thank you!