Implement database seeding

[quinnjr]

Description

Database seeding support for development and testing.

Tasks

• Create prax seed CLI command
• Support seed files in Rust or JSON
• Add factory/faker integration
• Support seed dependencies (order)
• Add prax seed:reset command

Example

// seeds/users.rs
use prax::seeder::*;

pub async fn run(db: &PraxClient) {
    db.user().create_many(vec![
        data! { email: "admin@example.com", role: "admin" },
        data! { email: "user@example.com", role: "user" },
    ]).exec().await?;
}