Summary

• Implements Website value object in the contact module
• Accepts http and https schemes only; rejects ftp, bare strings, etc.
• Normalises scheme and host to lowercase on construction via the url crate
• Adds is_https() and host() convenience accessors
• Adds url dependency to the contact feature flag

Type of change

• New value object / feature

Checklist

• Follows the ValueObject trait contract (new, value, into_inner)
• TryFrom<&str> implemented
• Display implemented
• serde support via cfg_attr
• Tests: valid input, empty input, invalid format, normalisation, try_from_str
• cargo fmt and cargo clippy clean
• cargo test --features contact passes

Closes #11