#78 feat: extract doc comments for OpenAPI descriptions

[RAprogramm]

Summary

• Add utils/docs.rs module for extracting doc comments from Rust attributes
• Parse /// comments from entity structs and fields
• Use entity doc comment as fallback for OpenAPI tag description

Usage

/// User account in the system.
///
/// Represents registered users with authentication info.
#[derive(Entity)]
#[entity(table = "users", api(tag = "Users"))]
pub struct User {
    #[id]
    pub id: Uuid,
    
    /// User's email address for authentication.
    #[field(create, update, response)]
    pub email: String,
}

In OpenAPI:

• Tag description: "User account in the system.\n\nRepresents registered users..."
• Field description: "User's email address for authentication."

Extracted Functions

• extract_doc_comments(attrs) - Get full doc comment as string
• extract_doc_summary(attrs) - Get first line only (for summaries)

Test plan

• 6 unit tests for doc extraction
• clippy clean
• Format check
• All 79 tests pass

Closes #78
Depends on #85

[codecov]

Codecov Report

❌ Patch coverage is 90.82569% with 10 lines in your changes missing coverage. Please review.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
...ates/entity-derive-impl/src/entity/parse/entity.rs	50.00%	3 Missing ⚠️
...rates/entity-derive-impl/src/entity/parse/field.rs	50.00%	3 Missing ⚠️
crates/entity-derive-impl/src/utils/docs.rs	96.87%	3 Missing ⚠️
...rates/entity-derive-impl/src/entity/api/openapi.rs	0.00%	1 Missing ⚠️

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