Switch CodeQL to advanced setup with autobuild for C# (#23)

Default setup used build-mode 'none' for C# which resulted in low
analysis quality (call target resolution 83% vs 85% threshold).
Switching to autobuild resolves NuGet dependencies properly.

Other languages (JS/TS, Python, Java) remain on build-mode 'none'.
Upgraded to security-extended query suite.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: goergenj

.github/workflows/codeql.yml

@@ -0,0 +1,48 @@
+name: "CodeQL"
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+  schedule:
+    - cron: "30 5 * * 1" # Weekly Monday 5:30 UTC
+
+jobs:
+  analyze:
+    name: Analyze (${{ matrix.language }})
+    runs-on: ${{ matrix.language == 'csharp' && 'ubuntu-latest' || 'ubuntu-latest' }}
+    permissions:
+      security-events: write
+      packages: read
+      actions: read
+      contents: read
+
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - language: csharp
+            build-mode: autobuild
+          - language: java-kotlin
+            build-mode: none
+          - language: javascript-typescript
+            build-mode: none
+          - language: python
+            build-mode: none
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Initialize CodeQL
+        uses: github/codeql-action/init@v4
+        with:
+          languages: ${{ matrix.language }}
+          build-mode: ${{ matrix.build-mode }}
+          queries: security-extended
+
+      - name: Perform CodeQL Analysis
+        uses: github/codeql-action/analyze@v4
+        with:
+          category: "/language:${{ matrix.language }}"