fix: drop \{ not: null }\ filters — Prisma 7 rejects them at runtime

PrismaClientValidationError ('Argument \`not\` must not be null') hit at
runtime when notifications-bridge mounted post-M12 schema change.
Although StringNullableFilter typings allow \`not: null\`, the v7 query
engine rejects it.

Removed the WHERE-side filter in 3 places — null-narrowing already
happens client-side via flatMap / Boolean filter:
- components/notifications/notifications-bridge.tsx
- app/api/realtime/notifications/route.ts
- lib/insights/verify-stats.ts (task_id filter)

Idea-questions / idea-jobs will be routed via separate channels in
T-502 + T-507; for now, story-question + task-job paths simply ignore
NULL rows in their post-fetch mapping.

Tests: 479/479 green; tsc clean.

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

app/api/realtime/notifications/route.ts

@@ -132,7 +132,9 @@ export async function GET(request: NextRequest) {
           status: 'open',
           expires_at: { gt: new Date() },
           product_id: { in: products.map((p) => p.id) },
-          story_id: { not: null },
+          // Skip idea-questions (story_id NULL) — story-questions only here.
+          // Narrowing happens in the flatMap below — Prisma 7 rejects
+          // `story_id: { not: null }` at runtime.
         },
         orderBy: { created_at: 'desc' },
         take: 100,