fix(cibg): address fieldset padding + atomic-design audit cleanup

Fix: address-fields shipped a scoped `fieldset { padding:0; margin:0 }` that
tied on specificity with CIBG's `.form-horizontal fieldset` and, injected later,
won — flattening the grey-box padding on "Mijn gegevens" and the registratie
wizard address step. Removed the override (kept the legend rule).

Audit cleanup (minimise atoms, converge or document near-duplicates):
- delete dead `app-card` (+ story; zero consumers, superseded by app-data-block)
  and the unused `.app-info-box` utility
- review-section raw <h2> -> app-heading; registratie-wizard lone <dl> -> app-data-block
- keep application-link's raw <h3> (vendored `.applications li a h3` chain needs
  the bare element) with an inline justification
- document the deliberate "don't merge these" verdicts in a new Convergence
  decisions table in atomic-design.mdx; record the card removal in cibg-gaps.mdx

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

src/styles.scss

@@ -128,13 +128,6 @@ body {
   color: var(--rhc-color-foreground-subtle);
 }
 
-/* Bordered info box (outline, no fill) — e.g. a "Vragen?" contact block. */
-.app-info-box {
-  border: var(--rhc-border-width-sm) solid var(--rhc-color-border-default);
-  border-radius: var(--rhc-border-radius-md);
-  padding: var(--rhc-space-max-xl);
-}
-
 /* Route transitions (withViewTransitions): cross-fade the routed CONTENT only.
    The chrome gets its own stable view-transition-name so it's lifted out of the
    `root` snapshot and stays put while the content fades. */