test: split vitest into node + nuxt projects and add a Postgres harness

Component/runtime specs (*.nuxt.spec.ts) run in the Nuxt environment; all
other specs run in a plain node environment where node_modules stay external,
so native CJS deps like `pg` load correctly (the Nuxt runtime inlines them and
breaks pg's internal `class … extends Pool`). Adds tests/helpers/db.ts, which
spins up and migrates a dedicated test database for repository integration
tests, and renames the board spec to the .nuxt suffix.

vitest.config.ts

@@ -1,9 +1,30 @@
+import { defineConfig } from 'vitest/config'
 import { defineVitestConfig } from '@nuxt/test-utils/config'
 
-export default defineVitestConfig({
+// Two projects, split by filename:
+//  • *.nuxt.spec.ts → run in the Nuxt runtime (components, anything needing
+//    auto-imports or the app environment).
+//  • everything else → a plain node environment. node_modules stay external,
+//    so native CJS deps like `pg` load correctly (the Nuxt runtime inlines them
+//    and breaks pg's internal `class … extends Pool`).
+export default defineConfig({
   test: {
-    // Default to a plain node environment; component/integration specs opt into
-    // the Nuxt runtime per-file with `// @vitest-environment nuxt`.
-    environment: 'node',
+    projects: [
+      {
+        test: {
+          name: 'server',
+          environment: 'node',
+          include: ['tests/**/*.spec.ts'],
+          exclude: ['tests/**/*.nuxt.spec.ts'],
+        },
+      },
+      defineVitestConfig({
+        test: {
+          name: 'nuxt',
+          environment: 'nuxt',
+          include: ['tests/**/*.nuxt.spec.ts'],
+        },
+      }),
+    ],
   },
 })