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

config/artemis.jsonc

@@ -8,11 +8,11 @@
   // ------------------------------------------------------------------------------
   "default": {
     "provider": "google",
-    "model": "gemini-3.6-flash",
+    "model": "gemini-3.7-flash",
     "thinking_level": "medium",
     "fallback": {
       "provider": "google",
-      "model": "gemini-3.5-flash",
+      "model": "gemini-3.6-flash",
       "thinking_level": "medium"
     }
   },
@@ -23,8 +23,8 @@
   "presets": {
     "gemini-flagship": {
       "provider": "google",
-      "model": "gemini-3.6-flash",
-      "fallback": { "provider": "google", "model": "gemini-3.5-flash" }
+      "model": "gemini-3.7-flash",
+      "fallback": { "provider": "google", "model": "gemini-3.6-flash" }
     },
     "gemini-flash": {
       "provider": "google",
@@ -54,7 +54,7 @@
   "nodes": {
     // 🧠 Planner: High-level goal decomposition and strategic step planning
     "planner": {
-      "thinking_level": "medium"
+      "thinking_level": "high"
     },
 
     // 🎯 Operator: Screen perception, element interaction, and direct execution