feat(db): add field_definition tables

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

crates/db/tests/migrate.rs

@@ -53,3 +53,21 @@ async fn migrate_creates_vocabulary_and_authority_tables(pool: PgPool) {
         );
     }
 }
+
+#[sqlx::test]
+async fn migrate_creates_field_definition_tables(pool: PgPool) {
+    let db = Db::from_pool(pool);
+
+    for table in ["field_definition", "field_definition_label"] {
+        let regclass: Option<String> =
+            sqlx::query_scalar(&format!("SELECT to_regclass('public.{table}')::text"))
+                .fetch_one(db.pool())
+                .await
+                .unwrap();
+        assert_eq!(
+            regclass.as_deref(),
+            Some(table),
+            "table {table} should exist"
+        );
+    }
+}