Add new page module and services; refactor existing entities

- Introduced a new page module with associated services.
- Refactored TypeORM entities in user and workspace modules.

server/src/core/page/dto/create-page.dto.ts

@@ -0,0 +1,18 @@
+import { IsOptional, IsString } from 'class-validator';
+
+export class CreatePageDto {
+  @IsOptional()
+  title?: string;
+
+  @IsOptional()
+  content?: string;
+
+  @IsOptional()
+  parentId?: string;
+
+  @IsString()
+  creatorId: string;
+
+  @IsString()
+  workspaceId: string;
+}

server/src/core/page/dto/update-page.dto.ts

@@ -0,0 +1,4 @@
+import { PartialType } from '@nestjs/mapped-types';
+import { CreatePageDto } from './create-page.dto';
+
+export class UpdatePageDto extends PartialType(CreatePageDto) {}