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>

backend/src/modules/auth/auth.module.ts

@@ -17,11 +17,13 @@ import { JwtStrategy } from './strategies/jwt.strategy';
 import { LocalStrategy } from './strategies/local.strategy';
 import { UsersModule } from '../users/users.module';
 import { OrganizationsModule } from '../organizations/organizations.module';
+import { IdeasModule } from '../ideas/ideas.module';
 
 @Module({
   imports: [
     UsersModule,
     OrganizationsModule,
+    IdeasModule,
     PassportModule,
     JwtModule.registerAsync({
       imports: [ConfigModule],