feat(db): add auth schema migrations (10 tables)

- users with partial unique index on (tenant_id, username) WHERE deleted_at IS NULL
- user_credentials, user_tokens with FK cascade
- roles, permissions with composite unique (tenant_id, code)
- role_permissions, user_roles junction tables
- organizations (self-ref tree), departments (tree + org FK), positions
- All tables include standard fields: id, tenant_id, timestamps, soft delete, version

crates/erp-server/migration/src/lib.rs

@@ -1,12 +1,34 @@
 pub use sea_orm_migration::prelude::*;
 
 mod m20260410_000001_create_tenant;
+mod m20260411_000002_create_users;
+mod m20260411_000003_create_user_credentials;
+mod m20260411_000004_create_user_tokens;
+mod m20260411_000005_create_roles;
+mod m20260411_000006_create_permissions;
+mod m20260411_000007_create_role_permissions;
+mod m20260411_000008_create_user_roles;
+mod m20260411_000009_create_organizations;
+mod m20260411_000010_create_departments;
+mod m20260411_000011_create_positions;
 
 pub struct Migrator;
 
 #[async_trait::async_trait]
 impl MigratorTrait for Migrator {
     fn migrations() -> Vec<Box<dyn MigrationTrait>> {
-        vec![Box::new(m20260410_000001_create_tenant::Migration)]
+        vec![
+            Box::new(m20260410_000001_create_tenant::Migration),
+            Box::new(m20260411_000002_create_users::Migration),
+            Box::new(m20260411_000003_create_user_credentials::Migration),
+            Box::new(m20260411_000004_create_user_tokens::Migration),
+            Box::new(m20260411_000005_create_roles::Migration),
+            Box::new(m20260411_000006_create_permissions::Migration),
+            Box::new(m20260411_000007_create_role_permissions::Migration),
+            Box::new(m20260411_000008_create_user_roles::Migration),
+            Box::new(m20260411_000009_create_organizations::Migration),
+            Box::new(m20260411_000010_create_departments::Migration),
+            Box::new(m20260411_000011_create_positions::Migration),
+        ]
     }
 }