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>

__tests__/actions/questions.test.ts

@@ -16,6 +16,9 @@ vi.mock('@/lib/prisma', () => ({
       findFirst: vi.fn(),
       updateMany: vi.fn(),
     },
+    product: {
+      findFirst: vi.fn().mockResolvedValue({ id: 'product-1' }),
+    },
   },
 }))
 
@@ -44,7 +47,13 @@ beforeEach(() => {
 describe('actions/questions — answerQuestion', () => {
   it('happy: status pending→answered, revalidatePath geroepen', async () => {
     mockGetSession.mockResolvedValue(SESSION_USER)
-    mockPrisma.claudeQuestion.findFirst.mockResolvedValueOnce({ id: VALID_ID }) // access-check
+    mockPrisma.claudeQuestion.findFirst.mockResolvedValueOnce({
+      id: VALID_ID,
+      story_id: 'story-1',
+      idea_id: null,
+      product_id: 'product-1',
+      idea: null,
+    })
     mockPrisma.claudeQuestion.updateMany.mockResolvedValueOnce({ count: 1 })
 
     const res = await answerQuestion(VALID_ID, VALID_ANSWER)
@@ -85,7 +94,13 @@ describe('actions/questions — answerQuestion', () => {
 
   it('al-answered: race-error met begrijpelijke melding', async () => {
     mockGetSession.mockResolvedValue(SESSION_USER)
-    mockPrisma.claudeQuestion.findFirst.mockResolvedValueOnce({ id: VALID_ID }) // access-check
+    mockPrisma.claudeQuestion.findFirst.mockResolvedValueOnce({
+      id: VALID_ID,
+      story_id: 'story-1',
+      idea_id: null,
+      product_id: 'product-1',
+      idea: null,
+    })
     mockPrisma.claudeQuestion.updateMany.mockResolvedValueOnce({ count: 0 })
     mockPrisma.claudeQuestion.findFirst.mockResolvedValueOnce({
       status: 'answered',
@@ -99,7 +114,13 @@ describe('actions/questions — answerQuestion', () => {
 
   it('verlopen: updateMany count=0, nog open status maar voorbij expiry', async () => {
     mockGetSession.mockResolvedValue(SESSION_USER)
-    mockPrisma.claudeQuestion.findFirst.mockResolvedValueOnce({ id: VALID_ID })
+    mockPrisma.claudeQuestion.findFirst.mockResolvedValueOnce({
+      id: VALID_ID,
+      story_id: 'story-1',
+      idea_id: null,
+      product_id: 'product-1',
+      idea: null,
+    })
     mockPrisma.claudeQuestion.updateMany.mockResolvedValueOnce({ count: 0 })
     mockPrisma.claudeQuestion.findFirst.mockResolvedValueOnce({
       status: 'open',