add web WASM Playwright harness for UI driving

tools/ui/ — scripts + Playwright config that let Claude Code (and
humans) drive the Flutter WASM build in a real browser. The point is
to avoid screenshot round-trips: every interactive widget in clide
ships a Semantics wrapper anyway (a11y requirement), so the automation
layer just queries the `flt-semantics[aria-label]` DOM.

  * build.sh — `flutter build web --wasm` from app/
  * serve.sh — `python3 -m http.server 4280` in the background.
    Before binding, kills any stale listener on the port (orphans
    from earlier failed runs no longer accumulate).
  * stop.sh — port-based kill; escalates to SIGKILL after 300ms.
    The pidfile is now advisory — port ownership is the source of
    truth.
  * driver.ts — `ClideDriver` class with `byLabel`, `click`, `type`,
    `readText`, `screenshot`, `dumpSemanticsTree`, and
    `waitUntilReady` that auto-clicks the `flt-semantics-placeholder`
    so the semantic tree is populated before queries.
  * tests/smoke.spec.ts — first driver test; asserts welcome +
    disconnected labels surface in the Semantics DOM.

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

tools/ui/README.md

@@ -0,0 +1,61 @@
+# clide UI harness
+
+A Playwright-based driver that drives the Flutter WASM build of clide
+through its semantic DOM tree (the same tree screen readers use).
+Used by Claude Code to "actually use the app" without screenshot
+round-trips, and by CI to catch web-regression bugs.
+
+## One-time setup
+
+```bash
+cd tools/ui
+npm install
+npx playwright install chromium
+```
+
+## Dev loop
+
+```bash
+# From repo root:
+make ui-dev                       # build web + start local server :4280
+cd tools/ui && npx playwright test
+
+# When done:
+make ui-stop                       # kill the local server
+```
+
+Or the one-shot smoke:
+
+```bash
+make ui-smoke                      # build + serve + run smoke + stop
+```
+
+## Driver surface
+
+```ts
+import { ClideDriver } from '../driver';
+
+test('...', async ({ page }) => {
+  const clide = new ClideDriver(page);
+  await clide.goto('/');
+
+  await clide.click('Open project');
+  await clide.type('Name', 'My project');
+  const text = await clide.readText('disconnected');
+
+  await clide.screenshot('out/my-state.png');
+  const tree = await clide.dumpSemanticsTree();
+});
+```
+
+All lookups go through Flutter's semantics tree (`flt-semantics[aria-label]`).
+This only works because every interactive widget in clide emits a
+`Semantics(label:, hint:, button:)` wrapper — a requirement that's baked
+in for screen-reader support and gets enforced by
+`test/a11y/semantic_coverage_test.dart`.
+
+## CI
+
+`make ui-smoke` is the CI entry — builds the WASM bundle, runs the
+harness, cleans up. Enabling Gitea Actions will start running this on
+every push.