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

mcp_server/notifiers/composite.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.
+
+"""Composite Notifier coordinating multi-channel notifications."""
+
+import logging
+from typing import Any
+
+from mcp_server.notifiers.agentapi import AgentApiNotifier
+from mcp_server.notifiers.base import BaseNotifier
+from mcp_server.notifiers.desktop import DesktopNotifier
+from mcp_server.notifiers.file import FileNotifier
+from mcp_server.notifiers.webhook import WebhookNotifier
+
+logger = logging.getLogger("mcp_server.notifiers.composite")
+
+
+class CompositeNotifier(BaseNotifier):
+    """Aggregates multiple notifiers and broadcasts events across all available channels."""
+
+    def __init__(self, notifiers: list[BaseNotifier] | None = None):
+        if notifiers is not None:
+            self._notifiers = notifiers
+        else:
+            self._notifiers = [
+                FileNotifier(),
+                AgentApiNotifier(),
+                WebhookNotifier(),
+                DesktopNotifier(),
+            ]
+
+    @property
+    def name(self) -> str:
+        return "composite"
+
+    def is_available(self) -> bool:
+        return any(n.is_available() for n in self._notifiers)
+
+    def register_notifier(self, notifier: BaseNotifier) -> None:
+        """Registers an additional custom notifier."""
+        self._notifiers.append(notifier)
+
+    def notify(
+        self,
+        conversation_id: str,
+        message: str,
+        title: str | None = None,
+        event_type: str = "completed",
+        payload: dict[str, Any] | None = None,
+    ) -> bool:
+        any_success = False
+        for notifier in self._notifiers:
+            if notifier.is_available():
+                try:
+                    success = notifier.notify(
+                        conversation_id=conversation_id,
+                        message=message,
+                        title=title,
+                        event_type=event_type,
+                        payload=payload,
+                    )
+                    if success:
+                        any_success = True
+                except Exception as e:
+                    logger.debug(f"Notifier '{notifier.name}' encountered error: {e}")
+
+        return any_success