fix: give each test worker its own SQLite database

Parallel Vitest workers were opening data/pichost.db together, so host-isolation failed with database is locked.

vitest.config.ts

@@ -3,6 +3,8 @@ import { defineConfig } from 'vitest/config'
 export default defineConfig({
   test: {
     environment: 'node',
-    include: ['server/**/*.test.ts']
+    include: ['server/**/*.test.ts'],
+    pool: 'forks',
+    setupFiles: ['./server/test/setup.ts']
   }
 })