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/components/layout/AppLayout.tsx

@@ -11,6 +11,7 @@ import {
   IconEyeOff,
   IconSun,
   IconMoon,
+  IconBulb,
 } from '@tabler/icons-react';
 import { Outlet, useNavigate, useLocation } from 'react-router-dom';
 import { useAuthStore } from '../../stores/authStore';
@@ -18,6 +19,7 @@ import { usePreferencesStore } from '../../stores/preferencesStore';
 import { Sidebar } from './Sidebar';
 import { AppTour } from '../onboarding/AppTour';
 import { OnboardingWizard } from '../onboarding/OnboardingWizard';
+import { IdeaModal } from '../ideas/IdeaModal';
 import logoSrc from '../../assets/logo.png';
 
 export function AppLayout() {
@@ -28,6 +30,10 @@ export function AppLayout() {
   const location = useLocation();
   const isImpersonating = !!impersonationOriginal;
 
+  // ── Ideation State ──
+  const [ideaModalOpened, { open: openIdeaModal, close: closeIdeaModal }] = useDisclosure(false);
+  const ideationEnabled = currentOrg?.settings?.ideationEnabled === true;
+
   // ── Onboarding State ──
   const [showTour, setShowTour] = useState(false);
   const [showWizard, setShowWizard] = useState(false);
@@ -121,6 +127,13 @@ export function AppLayout() {
             {currentOrg && (
               <Text size="sm" c="dimmed">{currentOrg.name}</Text>
             )}
+            {ideationEnabled && (
+              <Tooltip label="Submit an idea">
+                <ActionIcon variant="default" size="lg" onClick={openIdeaModal} aria-label="Submit idea">
+                  <IconBulb size={18} />
+                </ActionIcon>
+              </Tooltip>
+            )}
             <Tooltip label={colorScheme === 'dark' ? 'Light mode' : 'Dark mode'}>
               <ActionIcon
                 variant="default"
@@ -209,6 +222,9 @@ export function AppLayout() {
       {/* ── Onboarding Components ── */}
       <AppTour run={showTour} onComplete={handleTourComplete} />
       <OnboardingWizard opened={showWizard} onComplete={handleWizardComplete} />
+
+      {/* ── Ideation Modal ── */}
+      <IdeaModal opened={ideaModalOpened} onClose={closeIdeaModal} />
     </AppShell>
   );
 }