feat: add multi-device concurrency, server lifecycle CLI, and unified execution stream

- Implement DevicePool and DeviceExecutionLock concurrency modes (per-device FIFO vs global serialization)
- Extend ArtemisClient SDK and CLI with explicit device targeting and concurrency strategy configuration
- Add server lifecycle management (artemis restart, stop, status) with cross-platform PID discovery
- Update MCP server tools to support multi-device dispatch, trace tagging, and per-device execution
- Enhance Showcase UI with step-by-step visual replay, playback speed controls, and device serial badges
- Add comprehensive unit test coverage and edge-case verification scripts

artemis/interfaces/sdk/__init__.py

@@ -14,11 +14,14 @@
 
 """Python SDK for ARTEMIS."""
 
-from artemis.interfaces.sdk.client import ArtemisClient
-from artemis.interfaces.sdk.task import Task, TaskResult
+from artemis.interfaces.sdk.client import ArtemisClient, ConcurrencyMode
+from artemis.interfaces.sdk.task import StreamEvent, StreamEventType, Task, TaskResult
 
 __all__ = [
     "ArtemisClient",
+    "ConcurrencyMode",
+    "StreamEvent",
+    "StreamEventType",
     "Task",
     "TaskResult",
 ]