feat: Add Kits + FurnaceSplitter plugin config modules

DB migrations 016 (kits_configs) and 019 (furnacesplitter_configs) applied.
Backend: NestJS modules with CRUD, apply-to-server, import-from-server.
Frontend: Pinia stores, Vue views with config editor, router + nav wiring.
Kits view: 3-tab editor (list/editor/settings), kit items with shortname/amount/skinId/container.
FurnaceSplitter view: per-furnace toggles, split count, fuel multiplier settings.

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

backend-nest/src/modules/kits/dto/create-kits-config.dto.ts

@@ -0,0 +1,19 @@
+import { IsString, IsOptional, IsObject, MaxLength } from 'class-validator';
+import { ApiProperty, ApiPropertyOptional } from '@nestjs/swagger';
+
+export class CreateKitsConfigDto {
+  @ApiProperty({ example: 'Default Kits' })
+  @IsString()
+  @MaxLength(100)
+  config_name: string;
+
+  @ApiPropertyOptional({ example: 'Standard kit configuration' })
+  @IsString()
+  @IsOptional()
+  description?: string;
+
+  @ApiPropertyOptional()
+  @IsObject()
+  @IsOptional()
+  config_data?: Record<string, any>;
+}

backend-nest/src/modules/kits/dto/import-kits-config.dto.ts

@@ -0,0 +1,14 @@
+import { IsString, IsOptional, MaxLength } from 'class-validator';
+import { ApiProperty, ApiPropertyOptional } from '@nestjs/swagger';
+
+export class ImportKitsConfigDto {
+  @ApiProperty({ example: 'Server Import' })
+  @IsString()
+  @MaxLength(100)
+  config_name: string;
+
+  @ApiPropertyOptional({ example: 'Imported from live server' })
+  @IsString()
+  @IsOptional()
+  description?: string;
+}

backend-nest/src/modules/kits/dto/update-kits-config.dto.ts

@@ -0,0 +1,25 @@
+import { IsString, IsOptional, IsObject, IsBoolean, MaxLength } from 'class-validator';
+import { ApiPropertyOptional } from '@nestjs/swagger';
+
+export class UpdateKitsConfigDto {
+  @ApiPropertyOptional({ example: 'Updated Kits' })
+  @IsString()
+  @MaxLength(100)
+  @IsOptional()
+  config_name?: string;
+
+  @ApiPropertyOptional({ example: 'Updated description' })
+  @IsString()
+  @IsOptional()
+  description?: string;
+
+  @ApiPropertyOptional()
+  @IsObject()
+  @IsOptional()
+  config_data?: Record<string, any>;
+
+  @ApiPropertyOptional()
+  @IsBoolean()
+  @IsOptional()
+  is_active?: boolean;
+}