ci: add dependabot config and CodeQL workflow

Phase 1 W9 repo-hygiene task: enable continuous dependency scanning and

static analysis.

- .github/dependabot.yml: daily scans for pip (pyproject.toml) and

  github-actions ecosystems, grouped patch+minor updates, majors ignored

  for human review.

- .github/workflows/codeql.yml: weekly + on-push/PR CodeQL analysis for

  python and actions languages with security-and-quality query suite.

Private Vulnerability Disclosure repo setting is a GitHub UI toggle and

is tracked as a manual checklist item in the implementation log.

Author: petrsnd

.github/dependabot.yml

@@ -0,0 +1,33 @@
+version: 2
+updates:
+  - package-ecosystem: "pip"
+    directory: "/"
+    schedule:
+      interval: "daily"
+    open-pull-requests-limit: 10
+    labels:
+      - "dependencies"
+      - "security"
+    groups:
+      python-patch-and-minor:
+        update-types:
+          - "patch"
+          - "minor"
+    ignore:
+      - dependency-name: "*"
+        update-types:
+          - "version-update:semver-major"
+
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "daily"
+    open-pull-requests-limit: 5
+    labels:
+      - "dependencies"
+      - "ci"
+    groups:
+      actions-patch-and-minor:
+        update-types:
+          - "patch"
+          - "minor"

.github/workflows/codeql.yml

@@ -0,0 +1,51 @@
+name: "CodeQL"
+
+on:
+  push:
+    branches: [ "main" ]
+  pull_request:
+    branches: [ "main" ]
+  schedule:
+    - cron: "32 7 * * 1"
+
+jobs:
+  analyze:
+    name: Analyze (${{ matrix.language }})
+    runs-on: ubuntu-latest
+    timeout-minutes: 360
+    permissions:
+      security-events: write
+      packages: read
+      actions: read
+      contents: read
+
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - language: python
+            build-mode: none
+          - language: actions
+            build-mode: none
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Set up Python
+        if: matrix.language == 'python'
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.10"
+
+      - name: Initialize CodeQL
+        uses: github/codeql-action/init@v3
+        with:
+          languages: ${{ matrix.language }}
+          build-mode: ${{ matrix.build-mode }}
+          queries: security-and-quality
+
+      - name: Perform CodeQL Analysis
+        uses: github/codeql-action/analyze@v3
+        with:
+          category: "/language:${{ matrix.language }}"