feat: introduce MCP server, cross-platform runtime, and Showcase UI reorganization

- Showcase UI Reorganization:
  * Move web UI dashboard from root directory into apps/showcase_ui/ for cleaner project structure
  * Add 'artemis ui' CLI command (artemis/interfaces/cli/commands/ui.py) and launcher scripts for the interactive showcase console
- Standalone MCP Server & Notifiers (mcp_server/):
  * Implement dedicated MCP server package with mobile automation tools (device_state, inspect_trace, task_manager, task_runner)
  * Add multi-channel notifiers (AgentAPI, Desktop notifications, Webhooks, File output, and Composite routing)
  * Introduce background task runner and trace store for autonomous mobile execution monitoring
- Cross-Platform Runtime & Toolchain Support:
  * Add artemis/platform/ with OS-specific implementations for Linux, macOS (Darwin), and Windows
  * Add artemis/runtime/supervisor.py for resilient process and agent runtime supervision
  * Add artemis/toolchain/ with dependency resolution and SDK descriptors
  * Add cross-platform launcher scripts (start.sh, start.bat) and installer scripts (scripts/install_deps.*)
- Core Enhancements & Diagnostics:
  * Enhance coordinate normalization, OCR API fallback, and perception pipeline
  * Add credential validation (credentials_validator.py) and system diagnostics
  * Update bilingual documentation (README.md, README_CN.md) and architecture diagrams
- Test Suite Expansion:
  * Add integration tests for cloud gateway, remote ADB, and Artemis login
  * Add unit tests covering core diagnostics, platform detection, toolchain, credentials validator, optional OCR, and MCP tools

artemis/agents/validator/validator.py

@@ -47,6 +47,7 @@ from artemis.context import ArtemisContext, DeviceContext, DevicePlatform
 from artemis.controllers.unified_controller import UnifiedMobileController
 from artemis.data_engine.trace import CURRENT_TRACE_ID, trace
 from artemis.graph.state import State
+from artemis.platform import platform
 from artemis.services.llm import get_llm
 from artemis.tools.mobile.launch_app import find_package
 from artemis.utils import app_launch_utils, image_diff, visualization
@@ -153,7 +154,7 @@ class ValidatorNode:
                     local_ctx = ArtemisContext(
                         trace_id="local-fallback",
                         device=DeviceContext(
-                            host_platform="LINUX",
+                            host_platform=platform.os_type.name,
                             mobile_platform=DevicePlatform.ANDROID,
                             device_id=device_id,
                             device_width=w,