fix: Replace passlib with direct bcrypt implementation

• Remove passlib dependency and use bcrypt directly for password operations
• Update verify_password() to use bcrypt.checkpw() directly
• Update get_password_hash() to use bcrypt.hashpw() and bcrypt.gensalt()
• Pin BCrypt version to 4.0.1 for reproducible builds

close #85 #86

Full Changelog: v0.7.3...0.7.5