Make e2e tests independent and run them in parallel

Each test builds its pages in its own sandbox folder (search tests use a
random word), so tests no longer rely on earlier tests' leftovers and
run alone, in any order, or in parallel. The seed is just the home page.

Parallel load hid the htmx settle race from the timing-based tests, so
a dedicated test now submits a dialog in the task right after it is
inserted, which fails deterministically without the fix.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

e2e/playwright.config.js

@@ -4,9 +4,10 @@ const port = process.env.E2E_PORT || "8765";
 
 export default defineConfig({
   testDir: "tests",
-  // One seeded wiki is shared, and tests mutate it: run serially.
-  workers: 1,
-  fullyParallel: false,
+  // Tests share one server and wiki but each works in its own sandbox folder,
+  // so they can run in parallel.
+  workers: 4,
+  fullyParallel: true,
   reporter: "list",
   use: {
     baseURL: `http://127.0.0.1:${port}`,