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/showcase_ui/src/app/components/nav-switcher/nav-switcher.component.ts

@@ -0,0 +1,50 @@
+/**
+ * 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.
+ */
+
+import { Component } from '@angular/core';
+import { CommonModule } from '@angular/common';
+import { RouterLink, RouterLinkActive } from '@angular/router';
+
+@Component({
+  selector: 'app-nav-switcher',
+  standalone: true,
+  imports: [CommonModule, RouterLink, RouterLinkActive],
+  template: `
+    <nav class="floating-nav-switcher" aria-label="Main Navigation">
+      <a 
+        routerLink="/" 
+        routerLinkActive="active" 
+        [routerLinkActiveOptions]="{exact: true}"
+        class="nav-tab-btn"
+        title="Return to Home Launcher to start a new task"
+      >
+        <span class="material-symbols-outlined tab-icon">add_task</span>
+        <span class="tab-label">New / Home</span>
+      </a>
+      <a 
+        routerLink="/workspace" 
+        routerLinkActive="active" 
+        class="nav-tab-btn"
+        title="Open Workspace"
+      >
+        <span class="material-symbols-outlined tab-icon">space_dashboard</span>
+        <span class="tab-label">Workspace</span>
+      </a>
+    </nav>
+  `,
+  styleUrls: ['./nav-switcher.component.scss']
+})
+export class NavSwitcherComponent {}