feat(ST-901): add user.active_product_id with FK to Product

- Nullable relation User → Product with onDelete: SetNull
- Index on active_product_id for join performance
- Migration: 20260427165329_add_user_active_product_id
- Install @tanstack/react-table (was missing from node_modules)
- Fix PRIORITY_COLORS ref removed in earlier refactor
- Note: User schema change affects vendor/scrum4me-mcp submodule — run prisma generate + tsc --noEmit there after merge

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

components/backlog/pbi-list.tsx

@@ -232,7 +232,7 @@ export function PbiList({ productId, pbis, isDemo }: PbiListProps) {
                 onClick={() => setFilterPriority(null)}
                 className="flex items-center gap-1 text-xs text-primary hover:underline"
               >
-                <Badge className={cn('text-xs', PRIORITY_COLORS[filterPriority])}>
+                <Badge className="text-xs">
                   {PRIORITY_LABELS[filterPriority]}
                 </Badge>
                 <span>×</span>