feat(migrations): add compile-time migration generation

[RAprogramm]

Summary

• Add compile-time migration generation from Entity definitions
• Support full column constraints: unique, index, default, check, varchar
• Support composite indexes at entity level
• Support foreign key references with ON DELETE actions
• PostgreSQL DDL generation (CREATE TABLE, CREATE INDEX, DROP TABLE)

Usage

#[derive(Entity)]
#[entity(table = "users", migrations)]
pub struct User {
    #[id]
    pub id: Uuid,

    #[column(unique, index)]
    pub email: String,

    #[column(varchar = 100)]
    pub name: String,

    #[belongs_to(Organization, on_delete = "cascade")]
    pub org_id: Uuid,
}

// Generated:
// User::MIGRATION_UP - CREATE TABLE SQL
// User::MIGRATION_DOWN - DROP TABLE SQL

[codecov]

Codecov Report

❌ Patch coverage is 99.56772% with 6 lines in your changes missing coverage. Please review.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
...ntity-derive-impl/src/entity/parse/field/column.rs	99.11%	2 Missing ⚠️
...ity-derive-impl/src/entity/sql/postgres/helpers.rs	98.73%	2 Missing ⚠️
...erive-impl/src/entity/migrations/types/postgres.rs	99.42%	1 Missing ⚠️
...ity-derive-impl/src/entity/parse/entity/helpers.rs	99.57%	1 Missing ⚠️

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