feat(design): re-theme to CIBG Huisstijl (Bootstrap 5.2), replacing RHC/Utrecht

The portal now adheres to the CIBG design system (designsystem.cibg.nl) — a customized
Bootstrap 5.2 build — replacing the Rijkshuisstijl-Community / Utrecht theme. See ADR-0003.

- Vendor @cibg/huisstijl@3.22.0 under public/cibg-huisstijl/, loaded via a <link> in
  index.html (Storybook serves it via staticDirs). Drop the two @rijkshuisstijl-community deps.
- Token bridge in styles.scss: redefine the app's ~54 --rhc-* tokens onto CIBG/--bs-* values,
  so components keep referencing tokens (no 300+ site rewrite). System-font stack; licensed
  RO/Rijks text fonts intentionally not shipped.
- Re-skin every shared atom to Bootstrap/CIBG classes (btn, form-control, form-check-*,
  table, breadcrumb, …) keeping their input() APIs. alert is hand-rolled (CIBG drops .alert);
  local .card/.badge renamed to avoid Bootstrap collisions.
- Domain pages: drop stray rhc-*/utrecht-* classes; registration-table → table table-striped.

Verified: build green, check:tokens OK, lint clean, 174 tests pass, build-storybook OK,
and the served build loads the vendored CSS (200, .btn-primary present).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

public/cibg-huisstijl/LICENSE.txt

@@ -0,0 +1,22 @@
+CIBG Huisstijl Licences
+-----------------------
+
+The CIBG Huisstijl is free en MIT friendly. You can use it for applications build
+for the CIBG. Part is the assets used by the CIBG Huisstijl have a limited licence (see below).
+
+# Code: MIT License
+In the CIBG Huisstijl the MIT license applies to all non-font and non-icon files.
+
+# Fonts and images
+[Applicable to: All RO-SansWebText-* fonts, Rijklogo and favicons]
+By ministerial order of 16 June 2008 (Government Gazette 2008, no. 115), the State of the Netherlands
+(Ministry of General Affairs) entered a copyright reservation, as referred to in section 15b of the Copyright Act 1912,
+concerning the use and application of central government's general purpose Rijkslogo and visual identity, including the
+fonts Rijksoverheid Serif and Rijksoverheid Sans. This reservation does not apply to parties to whom central government
+has supplied the Rijkslogo and the visual identity for use in carrying out activities or services commissioned by
+central government. Any use in any form or by any means, electronic, mechanical, photocopying, recording or otherwise
+is prohibited unless prior written authorisation has been obtained from central government. To obtain authorisation,
+you should apply to the Government Information Service.
+
+# CIBG Icon font
+The CIBG Icon font is a combination of custom icons and Font Awesome icons. The MIT licence applies to this font.