Allow single-character names in validate_name

[taMaehashi]

Summary

This PR updates the validate_name regex to allow single-character names ({1,100} instead of {2,100}).

Motivation

Currently, names must be at least 2 characters long.
However, in many languages and cultures (especially East Asian ones), valid given names or family names can be only one character (e.g. 王, 李, 玲, 昇).
Not allowing single-character names can prevent real users from registering properly.

Change

• Modified validate_name regex:
  • from {2,100} → {1,100}

Impact

• Improves inclusivity for users with valid one-character names.
• Backward compatible: maximum length (100) and allowed characters remain unchanged.

Notes

This aligns with the project's past efforts (see PR #63) to support a wider variety of valid names worldwide.