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/ideas/ideas.module.ts

@@ -0,0 +1,14 @@
+import { Module } from '@nestjs/common';
+import { TypeOrmModule } from '@nestjs/typeorm';
+import { Idea } from './entities/idea.entity';
+import { Organization } from '../organizations/entities/organization.entity';
+import { IdeasController } from './ideas.controller';
+import { IdeasService } from './ideas.service';
+
+@Module({
+  imports: [TypeOrmModule.forFeature([Idea, Organization])],
+  controllers: [IdeasController],
+  providers: [IdeasService],
+  exports: [IdeasService],
+})
+export class IdeasModule {}