feat: Armarium full customization and 4-language i18n (v0.8.0)

Replaces Astro Rocket demo content with Armarium branding and adds
complete DE/FR/IT/EN translations across all pages.

Branding & content (v0.7.0):
- Add horizontal SVG logo to navbar with currentColor dark mode support
- Rewrite homepage with Armarium hero, 6 feature cards, trust bar,
  Zürich coat of arms SVG, and CTA; shared HomePage.astro component
- Add privacy page (/datenschutz) with 6 Infomaniak certification cards
  and 8-section policy (ISO 27001:2022, Swiss Hosting, nDSG/GDPR, etc.)
- Add legal notice page (/impressum)
- Rewrite about, contact, 404 pages with Armarium content
- Add features page (/projects) from projects content collection
- Add language switcher dropdown (LanguageSwitcherDropdown.astro)
- Add single launch blog post; remove all demo blog/project content
- Set up i18n foundation: astro.config.mjs, ui.ts, utils.ts

Full i18n (v0.8.0):
- Add all pages in FR/IT/EN: about, contact, blog, features, privacy,
  legal notice — 28 locale variants total
- Language switcher visible in every layout (PageLayout, BlogLayout,
  ProjectLayout, LandingLayout) with translated nav items
- Locale-aware nav and footer hrefs via nav.*.href keys in ui.ts
- Shared page components (AboutPage, ContactPage, FeaturesIndexPage,
  BlogIndexPage) accept locale prop; locale pages are 4-line wrappers
- Extend content.config.ts locale enum with de and it

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/assets/logo-horizontal.svg

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