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/test_credentials_validator.py

@@ -0,0 +1,80 @@
+# 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 pytest
+from unittest.mock import AsyncMock, patch, MagicMock
+from artemis.utils.credentials_validator import validate_api_key, _extract_error_message
+
+
+def test_extract_error_message():
+    resp_google = MagicMock()
+    resp_google.json.return_value = {"error": {"message": "API key invalid."}}
+    assert _extract_error_message(resp_google) == "API key invalid."
+
+    resp_openai = MagicMock()
+    resp_openai.json.return_value = {"message": "Incorrect API key."}
+    assert _extract_error_message(resp_openai) == "Incorrect API key."
+
+    resp_fallback = MagicMock()
+    resp_fallback.json.side_effect = Exception("JSON parse error")
+    resp_fallback.text = "Raw error text"
+    assert _extract_error_message(resp_fallback) == "Raw error text"
+
+
+@pytest.mark.asyncio
+async def test_validate_empty_and_placeholder():
+    is_valid, msg = await validate_api_key("google", "")
+    assert not is_valid
+    assert "empty" in msg.lower()
+
+    is_valid, msg = await validate_api_key("google", "API_KEY")
+    assert not is_valid
+    assert "placeholder" in msg.lower()
+
+
+@pytest.mark.asyncio
+async def test_validate_gemini_success():
+    with patch("httpx.AsyncClient.get", new_callable=AsyncMock) as mock_get:
+        mock_resp = MagicMock()
+        mock_resp.status_code = 200
+        mock_get.return_value = mock_resp
+
+        is_valid, msg = await validate_api_key("google", "valid_key_12345")
+        assert is_valid
+        assert "verified successfully" in msg
+
+
+@pytest.mark.asyncio
+async def test_validate_gemini_failure():
+    with patch("httpx.AsyncClient.get", new_callable=AsyncMock) as mock_get:
+        mock_resp = MagicMock()
+        mock_resp.status_code = 400
+        mock_resp.json.return_value = {"error": {"message": "API key not valid."}}
+        mock_get.return_value = mock_resp
+
+        is_valid, msg = await validate_api_key("google", "bad_key_12345")
+        assert not is_valid
+        assert "API key not valid" in msg
+
+
+@pytest.mark.asyncio
+async def test_validate_ocr_success():
+    with patch("httpx.AsyncClient.post", new_callable=AsyncMock) as mock_post:
+        mock_resp = MagicMock()
+        mock_resp.status_code = 200
+        mock_post.return_value = mock_resp
+
+        is_valid, msg = await validate_api_key("ocr", "valid_ocr_key_12345")
+        assert is_valid
+        assert "verified successfully" in msg