ci: add Dependabot with auto-merge for patch/minor updates

.github/dependabot.yml

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+version: 2
+updates:
+  # npm dependencies
+  - package-ecosystem: 'npm'
+    directory: '/'
+    schedule:
+      interval: 'daily'
+      time: '06:00'
+      timezone: 'Europe/London'
+    open-pull-requests-limit: 10
+    # Group minor/patch updates together to reduce PR noise
+    groups:
+      minor-and-patch:
+        patterns:
+          - '*'
+        update-types:
+          - 'minor'
+          - 'patch'
+    commit-message:
+      prefix: 'chore(deps)'
+    labels:
+      - 'dependencies'
+    # Auto-assign for review
+    reviewers:
+      - 'StuMason'
+
+  # GitHub Actions
+  - package-ecosystem: 'github-actions'
+    directory: '/'
+    schedule:
+      interval: 'weekly'
+      day: 'monday'
+      time: '06:00'
+      timezone: 'Europe/London'
+    commit-message:
+      prefix: 'ci(deps)'
+    labels:
+      - 'dependencies'
+      - 'github-actions'

.github/workflows/dependabot-auto-merge.yml

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+name: Dependabot Auto-Merge
+
+on:
+  pull_request:
+    types: [opened, synchronize, reopened]
+
+permissions:
+  contents: write
+  pull-requests: write
+
+jobs:
+  auto-merge:
+    runs-on: ubuntu-latest
+    if: github.actor == 'dependabot[bot]'
+
+    steps:
+      - name: Fetch Dependabot metadata
+        id: metadata
+        uses: dependabot/fetch-metadata@v2
+        with:
+          github-token: '${{ secrets.GITHUB_TOKEN }}'
+
+      - name: Auto-merge patch and minor updates
+        if: steps.metadata.outputs.update-type == 'version-update:semver-patch' || steps.metadata.outputs.update-type == 'version-update:semver-minor'
+        run: gh pr merge --auto --squash "$PR_URL"
+        env:
+          PR_URL: ${{ github.event.pull_request.html_url }}
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Comment on major updates
+        if: steps.metadata.outputs.update-type == 'version-update:semver-major'
+        run: |
+          gh pr comment "$PR_URL" --body "## Major Version Update
+
+          This PR contains a **major version update** which may include breaking changes.
+
+          **Please review carefully before merging:**
+          - [ ] Check the changelog for breaking changes
+          - [ ] Verify tests pass
+          - [ ] Test locally if needed
+
+          @StuMason - Manual review required."
+        env:
+          PR_URL: ${{ github.event.pull_request.html_url }}
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}