#79 feat: parse validation attributes for OpenAPI constraints

[RAprogramm]

Summary

• Add validation.rs module for parsing #[validate(...)] attributes
• Extract validation rules for conversion to OpenAPI schema constraints
• Store raw attributes for passthrough to generated DTOs

Supported Validators

Validator	OpenAPI Constraint
length(min = N)	minLength: N
length(max = N)	maxLength: N
range(min = N)	minimum: N
range(max = N)	maximum: N
email	format: email
url	format: uri
regex = "..."	pattern: ...

Usage

#[derive(Entity)]
#[entity(table = "users")]
pub struct User {
    #[id]
    pub id: Uuid,
    
    #[validate(length(min = 1, max = 255))]
    #[validate(email)]
    #[field(create, update, response)]
    pub email: String,
    
    #[validate(range(min = 0, max = 150))]
    #[field(create, update, response)]
    pub age: i32,
}

Generated OpenAPI Schema

email:
  type: string
  minLength: 1
  maxLength: 255
  format: email
age:
  type: integer
  minimum: 0
  maximum: 150

Test plan

• 8 unit tests for validation parsing
• clippy clean
• Format check
• All 87 tests pass

Closes #79
Depends on #86

[codecov]

Codecov Report

❌ Patch coverage is 91.37056% with 17 lines in your changes missing coverage. Please review.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
...y-derive-impl/src/entity/parse/field/validation.rs	94.14%	11 Missing ⚠️
...rates/entity-derive-impl/src/entity/parse/field.rs	33.33%	6 Missing ⚠️

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