test: add comprehensive unit, integration, and e2e test suites

Introduce complete test coverage for the ARTEMIS platform across multiple layers:
Unit tests: Add tests for agent nodes (Planner, Operator, Validator, Diagnoser, FlashRunner, Explorer), tools, utils (OCR/XML fusion, UI hierarchy), and data engine.
Integration tests: Add live tool verification, reactive runner, IME, and standalone workflow tests.
E2E tests: Add end-to-end scenario tests for media playback and failure recovery flows.
Fixtures & mocks: Add mock inputs (audio, video, screenshot) and test utilities.

tests/unit/test_context.py

@@ -0,0 +1,30 @@
+import asyncio
+import pytest
+from artemis.context import ArtemisContext, DeviceContext, DevicePlatform
+
+
+@pytest.mark.asyncio
+async def test_artemis_context_waits_for_background_tasks():
+    device = DeviceContext(
+        host_platform="LINUX",
+        mobile_platform=DevicePlatform.ANDROID,
+        device_id="dummy",
+        device_width=1080,
+        device_height=2400,
+    )
+
+    context = ArtemisContext(device=device)
+
+    task_run = False
+
+    async def dummy_task():
+        nonlocal task_run
+        await asyncio.sleep(0.1)
+        task_run = True
+
+    async with context:
+        task = asyncio.create_task(dummy_task())
+        context.background_tasks.append(task)
+
+    # After exiting the context, the task should have run to completion
+    assert task_run is True