Reorganize the catalog: engineering tools first, games and general utilities as secondary sections

[YurMil]

The homepage currently mixes EN/DIN engineering calculators with mini-games and general-purpose tools (file renamer, calendar generator, focus planner) in one catalog. Restructure so the landing page leads with the engineering toolset and the rest lives in clearly separated secondary sections.

Why: a mechanical engineer landing on the site should immediately recognize it as a professional calculation toolbox; unrelated tools dilute that first impression, while still being valuable enough to keep one click away.

Acceptance criteria:

• Landing page hero + first catalog block show engineering utilities only
• "Extras" (games, productivity tools) get their own section/pages with navigation entries
• Category metadata in src/data/utilities.ts drives the split (no hardcoded lists)
• Sitemap and internal links updated

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