phonebook-001 first commit

[Witch-dev]

No description provided.

[TheCSharpAcademy]

@Witch-dev Thanks for submitting! Unfortunately we can't approve at the moment as the project has no Readme. Also, since we're here, please address he following issues

PhoneNumber column configuration is wrong. In ContactDbContext, PhoneNumber is first configured as uniqueidentifier, then as nvachar(50). There’s also a typo: it should be nvarchar(50). This should be cleaned up before approval.

Duplicate phone numbers still get added AddContactToDb() checks if a phone number already exists, but it doesn’t return, so the duplicate contact is still inserted.

Name validation is missing Email and phone validation exist, but the name can be empty or whitespace. Add validation for this.

Phone validation can crash phoneUtil.Parse(number, null) can throw on invalid input. Use TryParse instead.