native press key, scroll, drag mouse (#78)

<!-- CURSOR_SUMMARY -->
> [!NOTE]
> Adds new input endpoints (press_key, scroll, drag_mouse), serializes
input actions, updates OpenAPI/client, installs xdotool, and
expands/refactors e2e tests with dependency bumps.
> 
> - **API/Backend**:
> - **New endpoints**: `POST /computer/press_key`, `POST
/computer/scroll`, `POST /computer/drag_mouse` with validation and
xdotool integration.
> - **Input serialization**: add `inputMu` to serialize
mouse/keyboard/screenshot actions; apply across `MoveMouse`,
`ClickMouse`, `TakeScreenshot`, `TypeText`.
> - **OpenAPI + Client**: extend `openapi.yaml`; regenerate `lib/oapi`
with new models/requests/responses and adjusted click button enums.
> - **Infrastructure**:
>   - **Dockerfile** (headless): install `xdotool`.
> - **Tests**:
> - Add `TestInputEndpointsSmoke`; modernize e2e tests (use `require`,
simplify flows) and minor cleanups.
> - **Dependencies**:
> - Bump `testify`, `golang.org/x/sync`, add `samber/lo`,
`golang.org/x/text`.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
2b85972. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Author: rgarcia

images/chromium-headless/image/Dockerfile

@@ -52,6 +52,7 @@ RUN set -xe; \
     dbus-x11 \
     xvfb \
     x11-utils \
+    xdotool \
     software-properties-common \
     supervisor;
 

server/cmd/api/api/api.go

@@ -36,6 +36,9 @@ type ApiService struct {
 	// DevTools upstream manager (Chromium supervisord log tailer)
 	upstreamMgr *devtoolsproxy.UpstreamManager
 	stz         scaletozero.Controller
+
+	// inputMu serializes input-related operations (mouse, keyboard, screenshot)
+	inputMu sync.Mutex
 }
 
 var _ oapi.StrictServerInterface = (*ApiService)(nil)