Bootstrap's CSS was overriding all Tailwind utility classes in production,
making parvagues render as raw unstyled HTML. Root cause: _app.js imported
bootstrap.css globally before globals.css (Tailwind v4).

- Remove bootstrap dependency and import from _app.js
- Remove stale tailwind.config.js (v3 format, ignored by v4)
- Remove @tailwindcss/aspect-ratio (v3 plugin, built-in in v4)
- Replace 3 Bootstrap `container` usages with Tailwind equivalents
- Scope main.css legacy element styles with :not(:has(.parvagues-root))
  to prevent link colors, section margins, footer styles from bleeding
  into parvagues pages
- Add .parvagues-root class to parvagues Layout for scoping