fix(core): exclude .stryker-tmp from vitest test discovery

vitest.config.ts

@@ -16,6 +16,8 @@ export default defineConfig({
       "**/dist/**",
       // Playwright's own e2e suite lives under src/bridges/user/web/e2e and is driven by `pnpm test:e2e`, not vitest -- its *.e2e.test.ts files would otherwise also match vitest's default **/*.test.ts discovery glob.
       "src/bridges/user/web/e2e/**",
+      // Stryker's own instrumented sandbox copies of the source (each mutant gets a full copy under .stryker-tmp/sandbox-*/), including its own nested copy of the e2e suite above -- the exclude pattern for that suite only matches the real src/ path, not this prefixed one, so running `pnpm test` (e.g. via the pre-push hook) while a mutation run's sandbox exists on disk picks up Playwright's own e2e tests and fails on `test.describe()` being called outside a Playwright config. Matches the same exclusion eslint.config.ts's `ignores` and stryker.config.ts's own `ignorePatterns` already carry, for the identical reason.
+      ".stryker-tmp/**",
     ],
   },
 });