feat: add support for flexible password policy

[ankita10119]

Description

Adds support for flexible password complexity policies with granular validation rules. This enhancement allows configuring password requirements based on character types, sequential/identical character restrictions, and length constraints.

Changes

New Interfaces & Types

• Added PasswordComplexityPolicy interface with configurable validation rules:
  • Character type requirements (uppercase, lowercase, numbers, special characters)
  • Minimum length validation
  • Identical character detection and blocking
  • Sequential character detection and blocking
  • Character type rule modes ("all" or "at_least")
• Extended DBConnection interface to include password_options.complexity configuration

Validation Logic

• Implemented validateWithComplexityPolicy() function with support for:
  • Minimum length enforcement
  • Repeated character detection (e.g., "aaa")
  • Sequential character detection (e.g., "abc", "123")
  • Character type validation with detailed per-rule feedback
• Added helper functions hasSequentialChars() and hasIdenticalChars() for pattern detection

Integration

• Updated signup and signup-password screens to:
  • Expose passwordComplexityPolicy in transaction members
  • Automatically use complexity policy validation when available
  • Fall back to legacy password policy validation for backward compatibility
• Added getPasswordComplexityPolicy() helper to extract policy from transaction context

Backward Compatibility

Maintains full backward compatibility by falling back to existing password policy validation when complexity policy is not configured.

Checklist

• I have added documentation for new/changed functionality in this PR or in auth0.com/docs
• All active GitHub checks for tests, formatting, and security are passing
• The correct base branch is being used, if not the default branch