fix: POST /suggestions requiere JWT (solo usuarios autenticados)

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

backend/src/suggestions/suggestions.controller.ts

@@ -10,6 +10,8 @@ export class SuggestionsController {
   constructor(private suggestions: SuggestionsService) {}
 
   @Post()
+  @UseGuards(JwtAuthGuard)
+  @ApiBearerAuth()
   create(@Body() dto: CreateSuggestionDto) {
     return this.suggestions.create(dto);
   }