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

start.bat

@@ -0,0 +1,35 @@
+@echo off
+rem Copyright 2026 Google LLC
+rem
+rem Licensed under the Apache License, Version 2.0 (the "License");
+rem you may not use this file except in compliance with the License.
+rem You may obtain a copy of the License at
+rem
+rem     http://www.apache.org/licenses/LICENSE-2.0
+rem
+rem Unless required by applicable law or agreed to in writing, software
+rem distributed under the License is distributed on an "AS IS" BASIS,
+rem WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+rem See the License for the specific language governing permissions and
+rem limitations under the License.
+
+chcp 65001 >nul 2>&1
+setlocal EnableDelayedExpansion
+title Artemis Mobile Agent UI
+
+cd /d "%~dp0"
+
+echo ======================================================
+echo       Artemis Autonomous Mobile Agent UI
+echo ======================================================
+echo.
+
+rem Run the PowerShell bootstrap with execution policy bypass
+powershell -NoProfile -ExecutionPolicy Bypass -File "%~dp0scripts\start.ps1" %*
+
+if %ERRORLEVEL% NEQ 0 (
+    echo.
+    echo An error occurred while starting Artemis.
+    pause
+)
+