Logo design (#7) (#9)

* style finish [skip ci]

* refine background gradient for page layout [skip ci]

* Add new logo assets and favicon for Humangehalt

- Added PNG and SVG versions of the Humangehalt logo featuring an "H" with a petrol-colored slash underlay.
- Introduced a new favicon in both ICO and SVG formats to enhance branding across platforms.

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authored-by: Bernhard Dorn <mail@bernharddorn.de>

Author: devdorn