Remove design-background highlight from the hero

[karedas]

Changes

• Remove only the purple Background / Percorso — Web design & UI fact from the English and Italian hero.
• Keep location, working arrangement and languages.
• Preserve design background elsewhere, all headings, styling and PDFs.
• Update regression tests for the three remaining facts and colour usage.

Validation

• Biome passed; 14 unit tests passed.
• Astro check and production build passed.
• 57 browser tests passed in the full run; the two colour tests had loaded the old expectation and both passed on rerun after updating it.
• Desktop/mobile layout and accessibility tests passed.

No merge performed.

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