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

tests/unit/core/test_platform.py

@@ -0,0 +1,78 @@
+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Unit tests for Platform Abstraction Layer (PAL)."""
+
+from pathlib import Path
+from unittest.mock import patch
+
+from artemis.platform import (
+    DarwinPlatform,
+    LinuxPlatform,
+    OSType,
+    WindowsPlatform,
+    get_platform,
+)
+
+
+def test_platform_singleton():
+    """Verify global platform singleton is initialized and conforms to protocol."""
+    p = get_platform()
+    assert p is not None
+    assert p.os_type in (OSType.LINUX, OSType.MACOS, OSType.WINDOWS)
+    assert p.paths.config_dir is not None
+    assert p.paths.data_dir is not None
+    assert p.paths.temp_dir() is not None
+    assert p.process.path_separator in (":", ";")
+
+
+def test_linux_platform_paths():
+    """Verify Linux platform paths conform to XDG Base Directory specification."""
+    with patch.dict(
+        "os.environ",
+        {"XDG_CONFIG_HOME": "/tmp/test_xdg_config", "XDG_DATA_HOME": "/tmp/test_xdg_data"},
+        clear=False,
+    ):
+        linux_p = LinuxPlatform()
+        assert linux_p.os_type == OSType.LINUX
+        assert linux_p.paths.config_dir == Path("/tmp/test_xdg_config/artemis")
+        assert linux_p.paths.data_dir == Path("/tmp/test_xdg_data/artemis")
+        assert linux_p.process.path_separator == ":"
+
+
+def test_darwin_platform_paths():
+    """Verify macOS platform paths adhere to Apple Library standards."""
+    darwin_p = DarwinPlatform()
+    assert darwin_p.os_type == OSType.MACOS
+    assert "Library/Application Support" in str(darwin_p.paths.config_dir)
+    assert darwin_p.process.path_separator == ":"
+
+
+def test_windows_platform_paths():
+    """Verify Windows platform paths adhere to AppData standards."""
+    with patch.dict(
+        "os.environ",
+        {
+            "APPDATA": "C:\\Users\\Test\\AppData\\Roaming",
+            "LOCALAPPDATA": "C:\\Users\\Test\\AppData\\Local",
+        },
+        clear=False,
+    ):
+        with patch.object(Path, "mkdir", return_value=None):
+            win_p = WindowsPlatform()
+            assert win_p.os_type == OSType.WINDOWS
+            assert str(win_p.paths.config_dir).startswith("C:\\Users\\Test\\AppData\\Roaming")
+            assert str(win_p.paths.data_dir).startswith("C:\\Users\\Test\\AppData\\Local")
+            assert win_p.process.path_separator == ";"
+            assert win_p.get_install_command("adb") == "winget install Google.PlatformTools"