Fix radio selection visual and trailing divider in data rows

- radio-group: the Utrecht radio paints its dot only with the
  `utrecht-radio-button--checked` class (not the native :checked); we set
  [checked] but not the class, so a selected radio looked empty. Bind the class
  too. The intake step-1 choice now visibly selects.
- data-row: drop the border-block-end on the last row (:host:last-child) so a
  summary ends cleanly instead of showing a trailing empty row (visible in the
  concepts discriminated-unions card).

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

src/app/shared/ui/radio-group/radio-group.component.ts

@@ -16,6 +16,7 @@ export interface RadioOption {
         <label class="utrecht-form-label utrecht-form-label--radio-button" style="display:flex;align-items:center;gap:0.5rem;padding:0.25rem 0">
           <input
             class="utrecht-radio-button"
+            [class.utrecht-radio-button--checked]="value === opt.value"
             type="radio"
             [name]="name()"
             [value]="opt.value"