feat: Add backend support for one-click Rust server deployment

Add deploy endpoint, DTO, NATS command publisher, and WebSocket bridge
subscription to support the one-click server deployment feature via the
companion agent.

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

backend-nest/src/modules/servers/dto/deploy-server.dto.ts

@@ -0,0 +1,41 @@
+import { IsString, IsInt, Min, Max, MinLength } from 'class-validator';
+import { ApiProperty } from '@nestjs/swagger';
+
+export class DeployServerDto {
+  @ApiProperty({ example: 'My Rust Server', description: 'Server hostname' })
+  @IsString()
+  server_name: string;
+
+  @ApiProperty({ example: 100, description: 'Maximum player slots' })
+  @IsInt()
+  @Min(1)
+  @Max(500)
+  max_players: number;
+
+  @ApiProperty({ example: 4000, description: 'World size (1000-8000)' })
+  @IsInt()
+  @Min(1000)
+  @Max(8000)
+  world_size: number;
+
+  @ApiProperty({ example: 12345, description: 'Map seed' })
+  @IsInt()
+  seed: number;
+
+  @ApiProperty({ example: 28015, description: 'Server game port' })
+  @IsInt()
+  @Min(1024)
+  @Max(65535)
+  server_port: number;
+
+  @ApiProperty({ example: 28016, description: 'RCON port' })
+  @IsInt()
+  @Min(1024)
+  @Max(65535)
+  rcon_port: number;
+
+  @ApiProperty({ example: 'changeme', description: 'RCON password (min 6 chars)' })
+  @IsString()
+  @MinLength(6)
+  rcon_password: string;
+}