Task: Fix <main> landmarks on about/privacy pages

Files modified:
- src/pages/about.astro
- src/pages/ru/about.astro
- src/pages/privacy.astro
- src/pages/ru/privacy.astro

Verification:
- npm run lint: 0 errors
- npm run build: success
- grep dist for <main> on about/privacy pages: all 4 files contain <main> tag

Pattern applied:
- Breadcrumb nav and page header remain outside <main>
- Content sections wrapped in <main> following GeneratorLayout.astro pattern