feat: add multi-platform CI testing matrix

- Add GitHub Actions workflow for cross-platform testing
- Test matrix: Ubuntu/macOS/Windows × Python 3.10/3.11/3.12
- Run full test suite on all platforms
- Verify basic functionality (GPU detection, memory info)
- Update README badge to show CI status

Improves platform compatibility confidence and catches platform-specific issues early.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.github/workflows/test.yml

@@ -0,0 +1,40 @@
+name: Multi-Platform Tests
+
+on:
+  push:
+    branches: [ master, main ]
+  pull_request:
+    branches: [ master, main ]
+
+permissions:
+  contents: read
+
+jobs:
+  test:
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest, macos-latest, windows-latest]
+        python-version: ["3.10", "3.11", "3.12"]
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up Python ${{ matrix.python-version }}
+        uses: actions/setup-python@v5
+        with:
+          python-version: ${{ matrix.python-version }}
+
+      - name: Install dependencies
+        run: |
+          python -m pip install --upgrade pip
+          pip install -e ".[dev]"
+
+      - name: Run tests
+        run: |
+          python -m pytest kaiwu/tests/ -v --ignore=kaiwu/tests/bench_tasks
+
+      - name: Test import and basic functionality
+        run: |
+          python -c "import kaiwu.core.sysinfo; info = kaiwu.core.sysinfo.get_sysinfo(); print(f'Platform test OK: GPU={info.gpu_name}, RAM={info.ram_total_gb:.1f}GB')"