feat: módulo de sugerencias (backend) + página pública /sugerencias (admin)

- Backend: POST /suggestions (público) + GET /suggestions (JWT admin)
- Admin: página pública /sugerencias con formulario de sugerencias
- schema.prisma: modelo suggestions
- AuthGuard + Sidebar: /sugerencias como ruta pública

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

backend/src/suggestions/suggestions.service.ts

@@ -0,0 +1,26 @@
+import { Injectable } from '@nestjs/common';
+import { PrismaService } from '../prisma/prisma.service';
+
+@Injectable()
+export class SuggestionsService {
+  constructor(private prisma: PrismaService) {}
+
+  create(data: { name?: string; message: string }) {
+    return this.prisma.suggestions.create({ data });
+  }
+
+  findAll(page = 1, limit = 50) {
+    const skip = (page - 1) * limit;
+    return Promise.all([
+      this.prisma.suggestions.findMany({
+        skip,
+        take: limit,
+        orderBy: { created_at: 'desc' },
+      }),
+      this.prisma.suggestions.count(),
+    ]).then(([data, total]) => ({
+      data,
+      meta: { total, page, limit, totalPages: Math.ceil(total / limit) || 1 },
+    }));
+  }
+}