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>

CHANGELOG.md

@@ -30,6 +30,7 @@ heading, and (b) bumping `project.yaml` `version:` in the same commit.
 
 ### Added
 
+- Web WASM harness under `tools/ui/` — Playwright driver so Claude Code (and humans) can drive the Flutter build in a real browser via the Semantics tree. `build.sh` / `serve.sh` / `stop.sh` manage a local `http.server` on `:4280` with port-based reclaim and kill (so orphaned listeners from earlier runs get swept). `driver.ts` exposes `ClideDriver` with `byLabel` / `click` / `type` / `readText` / `screenshot` / `dumpSemanticsTree` / `waitUntilReady` (auto-clicks the `flt-semantics-placeholder` to enable the semantics tree). First Playwright test `smoke.spec.ts` asserts welcome + disconnected labels render in the browser.
 - Integration tests under `app/integration_test/`, run with the `integration_test` package against the real built app (not an in-memory widget pump). The load-bearing startup gate lives here: `app_starts_test.dart` boots `ClideApp`, waits for the root shell to settle, and asserts the three-column layout + welcome tab + statusbar connection indicator all render. Also covers theme-picker modal open/select/dismiss (`theme_picker_test.dart`) and extension enable/disable lifecycle with contributions mounting/unmounting (`extension_lifecycle_test.dart`).
 - App-level test suite under `app/test/` — 168 tests across four layers:
   - **Unit** (`kernel/`, `extension/`) — events bus, settings (scope + YAML round-trip), log, i18n fallback chain matrix, theme resolver + loader + controller, panel registry + arrangement, command registry + keybinding parser + palette filter, extension-manager dep-order / cycle detection / enable-disable, manifest loader, extension scanner.