fix: align password policy to 8-72 printable ASCII on register (WealthLedger/backend#60)

Register accepts only printable ASCII (letters, digits, symbols, space),
8-72 characters, so characters equal bytes and the bcrypt 72-byte limit
holds without silent truncation. Login only caps the password at 72 bytes
so accounts created under the previous policy can still sign in.

CredentialsDto is split into RegisterDto and LoginDto; OpenAPI publishes
the register pattern and length bounds.

src/modules/auth/presentation/auth.dto.ts

@@ -1,8 +1,9 @@
 import { ApiProperty } from '@nestjs/swagger';
 import { Transform } from 'class-transformer';
 import {
+  IsNotEmpty,
   IsString,
-  MinLength,
+  Matches,
   Validate,
   ValidatorConstraint,
 } from 'class-validator';
@@ -13,8 +14,10 @@ const FIRST_CHARACTER_INDEX = 0;
 const MAX_EMAIL_LENGTH = 254;
 const ASCII_SPACE = 32;
 const ASCII_DELETE = 127;
-const MIN_PASSWORD_LENGTH = 12;
+// bcrypt reads at most 72 bytes; printable ASCII keeps characters == bytes.
+const MIN_PASSWORD_LENGTH = 8;
 const MAX_PASSWORD_BYTES = 72;
+const PASSWORD_PATTERN = `^[\\x20-\\x7E]{${MIN_PASSWORD_LENGTH},${MAX_PASSWORD_BYTES}}$`;
 
 @ValidatorConstraint({ name: 'email' })
 class EmailConstraint {
@@ -40,8 +43,9 @@ class EmailConstraint {
   }
 }
 
-@ValidatorConstraint({ name: 'passwordBytes' })
-class PasswordBytesConstraint {
+// Login stays lenient: accounts created under an older policy must still sign in.
+@ValidatorConstraint({ name: 'passwordMaxBytes' })
+class PasswordMaxBytesConstraint {
   validate(value: unknown): boolean {
     return (
       typeof value === 'string' &&
@@ -50,11 +54,11 @@ class PasswordBytesConstraint {
   }
 
   defaultMessage(): string {
-    return 'must not exceed 72 UTF-8 bytes';
+    return `must not exceed ${MAX_PASSWORD_BYTES} UTF-8 bytes`;
   }
 }
 
-export class CredentialsDto {
+class EmailDto {
   @ApiProperty({ example: 'user@example.com' })
   @IsString()
   @Transform(({ value }: { value: unknown }) =>
@@ -62,14 +66,28 @@ export class CredentialsDto {
   )
   @Validate(EmailConstraint)
   declare email: string;
+}
 
+export class RegisterDto extends EmailDto {
   @ApiProperty({
-    minLength: MIN_PASSWORD_LENGTH,
-    maxLength: MAX_PASSWORD_BYTES,
+    description: `Raw password: ${MIN_PASSWORD_LENGTH}-${MAX_PASSWORD_BYTES} printable ASCII characters (letters, digits, symbols, space). Not trimmed or normalized.`,
+    pattern: PASSWORD_PATTERN,
     example: 'a secure password',
   })
   @IsString()
-  @MinLength(MIN_PASSWORD_LENGTH)
-  @Validate(PasswordBytesConstraint)
+  @Matches(new RegExp(PASSWORD_PATTERN), {
+    message: `must be ${MIN_PASSWORD_LENGTH}-${MAX_PASSWORD_BYTES} printable ASCII characters`,
+  })
+  declare password: string;
+}
+
+export class LoginDto extends EmailDto {
+  @ApiProperty({
+    description: `Raw password, at most ${MAX_PASSWORD_BYTES} UTF-8 bytes. Not trimmed or normalized.`,
+    example: 'a secure password',
+  })
+  @IsString()
+  @IsNotEmpty()
+  @Validate(PasswordMaxBytesConstraint)
   declare password: string;
 }