feat(api): add OpenAPI/Swagger documentation for all API endpoints

Install @nestjs/swagger, configure Swagger UI at /api/docs with JWT bearer
auth, and add ApiTags/ApiOperation/ApiResponse/ApiProperty decorators to
all 8 controllers (50+ endpoints) and 31 DTOs across auth, listings,
search, payments, subscriptions, admin, notifications, and analytics modules.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

apps/api/src/modules/analytics/presentation/dto/get-price-trend.dto.ts

@@ -1,17 +1,22 @@
 import { IsArray, IsEnum, IsString } from 'class-validator';
+import { ApiProperty } from '@nestjs/swagger';
 import { Transform } from 'class-transformer';
 import { PropertyType } from '@prisma/client';
 
 export class GetPriceTrendDto {
+  @ApiProperty({ description: 'District name' })
   @IsString()
   district!: string;
 
+  @ApiProperty({ description: 'City name' })
   @IsString()
   city!: string;
 
+  @ApiProperty({ enum: PropertyType, description: 'Property type' })
   @IsEnum(PropertyType)
   propertyType!: PropertyType;
 
+  @ApiProperty({ description: 'Comma-separated list of periods', type: [String] })
   @IsArray()
   @IsString({ each: true })
   @Transform(({ value }) => (typeof value === 'string' ? value.split(',') : value))