Add pytest test suite and security scanning

- Add 33 tests for DiagnosticsRunner static methods (build_ssh_command,
  parse_output, parse_sysfs_stats, parse_ethtool and variants)
- Add test.yml CI workflow running pytest on every push/PR
- Add security.yml CI workflow running bandit on every push/PR (weekly)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.gitea/workflows/test.yml

@@ -0,0 +1,24 @@
+name: Test
+
+on:
+  push:
+    branches: ["**"]
+  pull_request:
+    branches: ["**"]
+
+jobs:
+  pytest:
+    name: Python Tests (pytest)
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+
+      - name: Install Python and dependencies
+        run: |
+          apt-get update -qq
+          apt-get install -y -qq python3 python3-pip
+          pip3 install pytest
+          pip3 install -r requirements.txt --quiet
+
+      - name: Run pytest
+        run: python3 -m pytest tests/ -v