fix(a11y): static accessibility findings (v1-readiness #4 — code-side)

Statische audit op happy-path-code; 4 categorieën gefixt vóór de Lighthouse-
verificatie die de gebruiker handmatig draait:

1. <main>-landmark op /login en /register (waren <div>); auth-pages krijgen
   nu een correcte landmark zodat screen-readers ze kunnen overslaan/nav

2. solo-task-card.tsx: agent-status-pill had role="button" + aria-label maar
   GEEN tabIndex en GEEN onKeyDown — keyboard-onbereikbaar. Nu compleet:
   tabIndex={0} + Enter/Space-handler

3. Form-label-associaties via htmlFor + id-pairs:
   - story-dialog (5): code, title, description, acceptance + priority via labelledby
   - task-dialog (3): title, description, implementation_plan
   - todo-list PromotePbi/PromoteStory dialogs (6): title, product, pbi, priority

   Lighthouse a11y "form-field-multiple-labels" en "label" rules worden
   hierdoor groen.

Niet aangeraakt:
- pbi-dialog: htmlFor was al goed gewired
- auth-form: htmlFor was al goed gewired
- Color-contrast: gebruikt MD3-tokens; theoretisch correct (verifieer in
  Lighthouse run)
- Heading-hierarchy: nog niet gescand — kan in vervolgronde

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

components/solo/solo-task-card.tsx

@@ -63,11 +63,19 @@ export function SoloTaskCard({ task, isDemo, onClick }: SoloTaskCardProps) {
         {job && (
           <span
             className={cn(
-              'text-[10px] px-1.5 py-0 rounded border flex items-center gap-1 shrink-0',
+              'text-[10px] px-1.5 py-0 rounded border flex items-center gap-1 shrink-0 cursor-pointer',
               JOB_STATUS_COLORS[job.status],
             )}
             onClick={(e) => { e.stopPropagation(); onClick() }}
+            onKeyDown={(e) => {
+              if (e.key === 'Enter' || e.key === ' ') {
+                e.preventDefault()
+                e.stopPropagation()
+                onClick()
+              }
+            }}
             role="button"
+            tabIndex={0}
             aria-label={`Agent-status: ${JOB_STATUS_LABELS[job.status]}`}
           >
             {JOB_STATUS_ACTIVE.has(job.status) && <Loader2 className="animate-spin" size={8} />}