fix(navigation): restore the reference 8px radius and unclip the mega menu

Traced against the running site (docker theme at AKSRT-theme) with real
computed styles:

- theme_main_radius defaulted to 12, so --main-radius was 12px and every
  dropdown panel, card and button was rounder than the reference, which
  sets 8px. Default is now 8 in the runtime reader and both schemas.
- The public bundle loads after main.min.css. Its bare img rule replaced
  the inline image baseline the menu relies on, and html{overflow-x} made
  the root a clipping context that crops the fixed senior mega menu.
  Reset is now scoped to content; the horizontal-overflow guard is on body.
- The senior mega menu renders a .container inside the dropdown where the
  reference keeps Bootstrap's 15px gutter; the padding-free site-shell
  .container rule stripped it, running the card/link grid to the edges.

Rebuilt public.css / public.min.css and the admin SPA.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

assets/css/core/reset.css

@@ -46,7 +46,6 @@ canvas {
 .header img,
 .mobile-header img {
   display: inline;
-  height: auto;
   vertical-align: middle;
 }