Accept fullName on registration

The register form collects a full name, but RegisterDto rejected it as
an unknown field under the global whitelist validation pipe, so
registration always failed 400 whenever a name was entered.

src/auth/auth.service.ts

@@ -40,7 +40,8 @@ export class AuthService {
     if (existing) throw new BadRequestException("Email already registered.");
 
     const passwordHash = this.hashPassword(payload.password);
-    const user = await this.prisma.user.create({ data: { email, passwordHash } });
+    const fullName = payload.fullName?.trim() || undefined;
+    const user = await this.prisma.user.create({ data: { email, passwordHash, fullName } });
     await this.prisma.auditLog.create({ data: { userId: user.id, action: "auth.register", metadata: { email } } });
 
     const verifyToken = crypto.randomBytes(32).toString("hex");

src/auth/dto/register.dto.ts

@@ -1,4 +1,4 @@
-import { IsEmail, IsString, MinLength } from "class-validator";
+import { IsEmail, IsOptional, IsString, MaxLength, MinLength } from "class-validator";
 
 export class RegisterDto {
   @IsEmail({}, { message: "Invalid email address." })
@@ -7,4 +7,9 @@ export class RegisterDto {
   @IsString()
   @MinLength(8, { message: "Password must be at least 8 characters." })
   password!: string;
+
+  @IsOptional()
+  @IsString()
+  @MaxLength(200)
+  fullName?: string;
 }