- Validator moves to app/validators/projects/identifier_validator.rb
as Projects::IdentifierValidator. The path-style symbol on the
validates declaration ('projects/identifier') resolves to it.
Distinguishes domain-specific validators from globally reusable
ones (UrlValidator, JsonValidator, etc).
- Spec moves to spec/validators/projects/identifier_validator_spec.rb.
- Trim comments that explained framework conventions (validator
lookup, declaration order). Keep comments only where the WHY is
non-obvious to a Rails-fluent reader.