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/controllers/unified_controller.py

@@ -206,12 +206,11 @@ class UnifiedMobileController:
             for _ in range(nb_chars):
                 await self._driver.press_key("delete")
             return True
-        # Safe & robust full clear: Move to End -> Shift+Home selection -> Delete -> Fallback backspaces
+        # Best-effort full clear: End -> Ctrl+A -> Delete
         try:
             clear_cmd = (
                 "input keyevent 123 && "
-                "input keyevent --meta 1 122 && "
-                "input keyevent 67 && "
+                "input keycombination 113 29 && input keyevent 67 && "
                 "input keyevent 67 67 67 67 67 67 67 67 67 67 67 67 67 67 67 67 67 67 67 67"
             )
             await self._driver.execute_shell(clear_cmd)