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/mcp/test_notifiers.py

@@ -0,0 +1,131 @@
+# 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 MCP Multi-Environment Notifiers."""
+
+import json
+import os
+import shutil
+import tempfile
+import pytest
+
+from mcp_server.notifiers import (
+    BaseNotifier,
+    CompositeNotifier,
+    DesktopNotifier,
+    FileNotifier,
+    WebhookNotifier,
+    notify,
+)
+from mcp_server.utils import trace_store
+
+
+class DummyNotifier(BaseNotifier):
+    def __init__(self, available: bool = True, return_val: bool = True):
+        self._available = available
+        self._return_val = return_val
+        self.called_with = None
+
+    @property
+    def name(self) -> str:
+        return "dummy"
+
+    def is_available(self) -> bool:
+        return self._available
+
+    def notify(self, conversation_id, message, title=None, event_type="completed", payload=None):
+        self.called_with = {
+            "conversation_id": conversation_id,
+            "message": message,
+            "title": title,
+            "event_type": event_type,
+            "payload": payload,
+        }
+        return self._return_val
+
+
+def test_file_notifier():
+    temp_dir = tempfile.mkdtemp()
+    try:
+        trace_id = "test-file-trace-123"
+        trace_dir = os.path.join(temp_dir, trace_id)
+        os.makedirs(trace_dir, exist_ok=True)
+
+        notifier = FileNotifier()
+        with pytest.MonkeyPatch.context() as mp:
+            mp.setattr(trace_store, "TRACES_DIR", temp_dir)
+            success = notifier.notify(
+                conversation_id="conv-1",
+                message="Task completed",
+                title="Done",
+                event_type="completed",
+                payload={"trace_id": trace_id},
+            )
+            assert success is True
+
+            log_file = os.path.join(trace_dir, "notifications.jsonl")
+            assert os.path.exists(log_file)
+            with open(log_file, encoding="utf-8") as f:
+                lines = f.readlines()
+                assert len(lines) == 1
+                entry = json.loads(lines[0])
+                assert entry["event_type"] == "completed"
+                assert entry["message"] == "Task completed"
+    finally:
+        shutil.rmtree(temp_dir, ignore_errors=True)
+
+
+def test_webhook_notifier_not_configured(monkeypatch):
+    for var in WebhookNotifier.ENV_VARS:
+        monkeypatch.delenv(var, raising=False)
+    notifier = WebhookNotifier()
+    assert notifier.is_available() is False
+    assert notifier.notify("conv-1", "hello") is False
+
+
+def test_desktop_notifier_not_enabled(monkeypatch):
+    monkeypatch.delenv("ARTEMIS_DESKTOP_NOTIFY", raising=False)
+    notifier = DesktopNotifier()
+    assert notifier.is_available() is False
+
+
+def test_composite_notifier_dispatch():
+    d1 = DummyNotifier(available=True, return_val=True)
+    d2 = DummyNotifier(available=False, return_val=False)
+    d3 = DummyNotifier(available=True, return_val=True)
+
+    composite = CompositeNotifier(notifiers=[d1, d2, d3])
+    assert composite.is_available() is True
+
+    result = composite.notify(
+        conversation_id="conv-abc",
+        message="Hello World",
+        title="Test Title",
+        event_type="completed",
+        payload={"key": "val"},
+    )
+    assert result is True
+    assert d1.called_with is not None
+    assert d1.called_with["conversation_id"] == "conv-abc"
+    assert d2.called_with is None
+    assert d3.called_with is not None
+
+
+def test_global_notify_function():
+    res = notify(
+        conversation_id="conv-xyz",
+        message="Test message",
+        payload={"trace_id": "test-trace"},
+    )
+    assert isinstance(res, bool)