Tooling: Switch vitest to happy-dom (faster DOM env)

- happy-dom's per-file DOM-environment setup is ~half jsdom's cost (the dominant phase for our ~3300 tests) - ~22% faster on a plain/watch run; the gated (coverage) run is a smaller but real win. All 3318 tests pass under it.
- jsdom kept installed as the per-file fallback (`// @vitest-environment jsdom`) since happy-dom implements a subset of its APIs; knip is fine with it.
- happy-dom added via `--trust-policy-exclude chokidar --trust-policy-exclude semver` (both mainstream transitive deps whose old versions predate npm provenance; see pnpm-workspace.yaml).

Author: vdavid

apps/desktop/package.json

@@ -64,6 +64,7 @@
     "eslint-config-prettier": "^10.1.8",
     "eslint-plugin-svelte": "^3.17.1",
     "globals": "^17.5.0",
+    "happy-dom": "^20.9.0",
     "jsdom": "^29.0.2",
     "knip": "^6.7.0",
     "oxlint": "^1.61.0",

apps/desktop/vitest.config.ts

@@ -7,7 +7,12 @@ export default defineConfig({
   plugins: [Icons({ compiler: 'svelte' }), svelte()],
   test: {
     include: ['src/**/*.test.ts', 'scripts/**/*.test.js', 'test/e2e-shared/**/*.test.ts'],
-    environment: 'jsdom',
+    // happy-dom over jsdom: its per-file DOM-environment setup is roughly half
+    // the cost (the dominant phase for our ~3300 tests), ~22% faster on a plain
+    // run. All tests pass under it. Caveat: happy-dom implements a *subset* of
+    // jsdom's APIs — if a future test fails on a missing DOM API, switch that
+    // file back with `// @vitest-environment jsdom` (jsdom stays installed).
+    environment: 'happy-dom',
     globals: true,
     setupFiles: ['./src/test-setup.ts'],
     execArgv: ['--localstorage-file=.vitest-localstorage'],