Fix domain validation rejecting valid domains (#113)

[shigahi]

Problem

Closes #113.

isValidDomain rejected several valid domains, e.g.:

• test.app1e.com — a subdomain label containing a digit
• short labels like x.io

Root cause

The previous regex only allowed alphanumerics in the first label and restricted every following label to letters only ((?:\.[a-zA-Z]{2,})+). So any non-first / non-TLD label containing a digit (app1e) was rejected, and the first label was forced to be at least 3 characters.

/^((https:\/\/)|(http:\/\/))?[a-zA-Z0-9][a-zA-Z0-9-]{1,61}[a-zA-Z0-9](?:\.[a-zA-Z]{2,})+(\/)?$/

Fix

Validate each label independently (alphanumeric plus hyphens, no leading/trailing hyphen, max 63 chars) and restrict only the TLD to letters:

/^(https?:\/\/)?([a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?\.)+[a-zA-Z]{2,}\/?$/

Verification

• Now valid: test.app1e.com, app1e.kr, x.io, a.b.c.example.com, 1example.com, https://test.app1e.com, example.co.uk
• Still rejected: ``, example., `-bad.com`, `bad-.com`, `a..b.com`, `example.123`
• npm run build passes