fix(m12): user can answer idea-questions — inline + bell support

Two gaps discovered during the first live grill-session of IDEA-002:
the agent posted a question, but the user had no UI to answer it.
1. Idea-questions only appeared on the Timeline-tab as read-only entries
2. Notifications-bell fetched + handled story-questions only

This fix:

**Inline answer-form in IdeaTimeline** (components/ideas/idea-timeline.tsx)
- Open questions now render an AnswerForm directly under the question text
- Multi-choice options become clickable buttons (one-click submit); free-text
  fallback via collapsed details/textarea
- Plain free-text questions render textarea + Verzend
- Calls existing answerQuestion server-action; toast + router.refresh on success

**Notifications-bell extended for idea-questions**
- stores/notifications-store.ts: NotificationQuestion → discriminated union
  (kind: 'story' | 'idea'); forYouCount treats idea-questions as always-for-you
  (idea is strictly user_id-only — only the owner sees them)
- components/notifications/notifications-bridge.tsx: parallel fetch of
  story-questions (productAccessFilter) + idea-questions (idea.user_id ===
  session.userId); merged + sorted by created_at
- components/notifications/notifications-sheet.tsx: renders idea_code/title
  for kind='idea'
- components/notifications/answer-modal.tsx: header + open-link branch on
  kind (idea → /ideas/[id]?tab=timeline; story → existing /sprint link)
- lib/realtime/use-notifications-realtime.ts: idea-question events also
  trigger close+reconnect on 'open' (loads fresh detail) and remove(id) on
  non-open — same pattern story-questions already use
- components/shared/notifications-bell.tsx: badge counts idea-questions as
  for-you regardless of assignee

**Security gap closed (actions/questions.ts answerQuestion)**
Before: accepted any answer if user has product-access.
After: idea-questions require idea.user_id === session.userId; story-
questions keep the existing productAccessFilter path. (Prisma 7 rejects
\`{ not: null }\` in WHERE; routing happens app-level after a single fetch.)

Tests: 546/546 still green.

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

lib/realtime/use-notifications-realtime.ts

@@ -138,6 +138,14 @@ export function useNotificationsRealtime() {
               assignee_id: payload.assignee_id,
               status: payload.status,
             })
+            // M12 hotfix: óók in notifications-bel. Open → reconnect zodat
+            // initial-state de full question-detail levert; non-open → remove.
+            if (payload.status === 'open') {
+              close()
+              connect()
+            } else {
+              remove(payload.id)
+            }
             return
           }