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

apps/admin_console/services/device_stream_service.py

@@ -24,6 +24,8 @@ import subprocess
 import time
 from collections.abc import AsyncGenerator
 
+from artemis.toolchain import find_adb
+
 logger = logging.getLogger("artemis.stream_service")
 
 
@@ -41,8 +43,9 @@ class DeviceStreamService:
     async def get_device_serial(self) -> str | None:
         """Find the currently connected active ADB device serial."""
         try:
+            adb_bin = find_adb()
             proc = await asyncio.create_subprocess_exec(
-                "adb",
+                adb_bin,
                 "devices",
                 stdout=subprocess.PIPE,
                 stderr=subprocess.PIPE,
@@ -64,10 +67,11 @@ class DeviceStreamService:
             try:
                 start_t = time.time()
                 serial = await self.get_device_serial()
+                adb_bin = find_adb()
                 cmd = (
-                    ["adb", "-s", serial, "exec-out", "screencap", "-p"]
+                    [adb_bin, "-s", serial, "exec-out", "screencap", "-p"]
                     if serial
-                    else ["adb", "exec-out", "screencap", "-p"]
+                    else [adb_bin, "exec-out", "screencap", "-p"]
                 )
                 proc = await asyncio.create_subprocess_exec(
                     *cmd,