fix: optimize test infrastructure and fix missing brand migration

- Share PGlite instance per test file (TRUNCATE RESTART IDENTITY instead
  of creating new instance per test) — tests run in ~9s vs minutes
- Add missing 'brand' column to items table migration
- Fix corrupt 0002 snapshot (merge conflict artifacts)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/helpers/db.ts

@@ -1,16 +1,51 @@
 import { PGlite } from "@electric-sql/pglite";
+import { sql } from "drizzle-orm";
 import { drizzle } from "drizzle-orm/pglite";
 import { migrate } from "drizzle-orm/pglite/migrator";
 import * as schema from "../../src/db/schema.ts";
 
 type Db = ReturnType<typeof drizzle<typeof schema>>;
 
-export async function createTestDb() {
-	const client = new PGlite();
-	const db = drizzle(client, { schema });
+// Cache: one PGlite instance per test file (per worker)
+let cachedClient: PGlite | null = null;
+let cachedDb: Db | null = null;
 
-	// Apply all migrations to create tables
-	await migrate(db, { migrationsFolder: "./drizzle-pg" });
+async function getOrCreateDb(): Promise<Db> {
+	if (cachedDb) return cachedDb;
+	cachedClient = new PGlite();
+	cachedDb = drizzle(cachedClient, { schema });
+	await migrate(cachedDb, { migrationsFolder: "./drizzle-pg" });
+	return cachedDb;
+}
+
+// Truncation order respects foreign keys (children first)
+const TRUNCATE_TABLES = [
+	"setup_items",
+	"setups",
+	"thread_candidates",
+	"threads",
+	"items",
+	"global_item_tags",
+	"global_items",
+	"tags",
+	"oauth_tokens",
+	"oauth_codes",
+	"oauth_clients",
+	"api_keys",
+	"settings",
+	"categories",
+	"users",
+];
+
+export async function createTestDb() {
+	const db = await getOrCreateDb();
+
+	// Truncate all tables and reset sequences (fast reset, no PGlite restart)
+	for (const t of TRUNCATE_TABLES) {
+		await db.execute(
+			sql.raw(`TRUNCATE TABLE "${t}" RESTART IDENTITY CASCADE`),
+		);
+	}
 
 	// Seed a test user
 	const [user] = await db