Exclude the tsc build output from vitest instead of from the build

Excluding src/common tests from tsconfig.common.json kept vitest from
running the compiled copies twice, but it also meant those test files were
no longer type checked at all by `tsc --build` (eslint only catches lint
issues, not type errors).

Exclude common-ts-dist from test discovery instead, so the tests are both
type checked and run exactly once.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01YCf7BBiPqNLUjVoN7rTCF6

tsconfig.common.json

@@ -16,9 +16,4 @@
   "include": [
     "src/common/**/*",
   ],
-  // tests are run by vitest from the sources; don't emit them into the build output,
-  // or vitest would discover and run the compiled copies too
-  "exclude": [
-    "src/common/**/*.test.ts",
-  ],
 }

tsconfig.node.json

@@ -11,6 +11,7 @@
   },
   "include": [
     "electron.vite.config.ts",
+    "vitest.config.ts",
     "i18next.config*.ts",
     "script/**/*",
   ],

vitest.config.ts

@@ -0,0 +1,9 @@
+import { configDefaults, defineConfig } from 'vitest/config';
+
+export default defineConfig({
+  test: {
+    // `tsc --build` compiles src/common (tests included) into common-ts-dist. Don't discover those
+    // compiled copies, or every test in src/common would also run a second time from the build output.
+    exclude: [...configDefaults.exclude, 'common-ts-dist/**'],
+  },
+});