feat: add ideation feature with per-tenant toggle

Adds idea submission capability gated by a per-tenant feature flag.
Super admins can enable/disable ideation for specific tenants via the
admin tenant detail drawer. Users see a lightbulb icon in the header
when enabled, opening a modal to submit ideas (title + description).
Ideas are stored in shared schema for cross-tenant backlog querying.

- Database: shared.ideas table (018-ideas.sql migration)
- Backend: Ideas NestJS module (entity, service, controller)
- Admin API: GET /admin/ideas, PUT /admin/ideas/:id/status,
  PUT /admin/organizations/:id/settings
- Frontend: IdeaModal component, lightbulb ActionIcon in header
- Admin UI: Feature Toggles card with ideation Switch in drawer

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

frontend/src/pages/admin/AdminPage.tsx

@@ -11,7 +11,7 @@ import {
   IconCrown, IconPlus, IconArchive, IconChevronDown,
   IconCircleCheck, IconBan, IconArchiveOff, IconDashboard,
   IconHeartRateMonitor, IconSparkles, IconCalendar, IconActivity,
-  IconCurrencyDollar, IconClipboardCheck, IconLogin, IconEye,
+  IconCurrencyDollar, IconClipboardCheck, IconLogin, IconEye, IconBulb,
 } from '@tabler/icons-react';
 import { useQuery, useMutation, useQueryClient } from '@tanstack/react-query';
 import { useNavigate } from 'react-router-dom';
@@ -211,6 +211,16 @@ export function AdminPage() {
     },
   });
 
+  const toggleIdeation = useMutation({
+    mutationFn: async ({ orgId, enabled }: { orgId: string; enabled: boolean }) => {
+      await api.put(`/admin/organizations/${orgId}/settings`, { ideationEnabled: enabled });
+    },
+    onSuccess: () => {
+      queryClient.invalidateQueries({ queryKey: ['admin-tenant-detail', selectedOrgId] });
+      queryClient.invalidateQueries({ queryKey: ['admin-orgs'] });
+    },
+  });
+
   const impersonateUser = useMutation({
     mutationFn: async (userId: string) => {
       const { data } = await api.post(`/admin/impersonate/${userId}`);
@@ -782,6 +792,27 @@ export function AdminPage() {
               </SimpleGrid>
             </Card>
 
+            <Card withBorder>
+              <Text fw={600} mb="xs">Feature Toggles</Text>
+              <Group justify="space-between">
+                <Group gap="xs">
+                  <IconBulb size={16} />
+                  <div>
+                    <Text size="sm">Ideation</Text>
+                    <Text size="xs" c="dimmed">Allow users to submit feature ideas</Text>
+                  </div>
+                </Group>
+                <Switch
+                  checked={tenantDetail.organization.settings?.ideationEnabled === true}
+                  onChange={(e) => {
+                    if (selectedOrgId) {
+                      toggleIdeation.mutate({ orgId: selectedOrgId, enabled: e.currentTarget.checked });
+                    }
+                  }}
+                />
+              </Group>
+            </Card>
+
             <Card withBorder>
               <Text fw={600} mb="xs">Subscription</Text>
               <Stack gap="xs">