chore: improve dependabot configuration (#619)

- Add grouped dependency updates for root Gradle (ktor, kotlinx, kotlin,
kotest, testing, infrastructure, gradle-plugins)
- Track all sample projects via `directories: /samples/*` with separate
PRs for ktor, kotlin, and mcp-kotlin-sdk
- Track npm dependencies in integration tests
- Group github actions updates into a single PR

## Types of changes
- [ ] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality to change)
- [ ] Documentation update

## Checklist
- [x] I have read the [MCP
Documentation](https://modelcontextprotocol.io)
- [x] My code follows the repository's style guidelines
- [x] New and existing tests pass locally
- [ ] I have added appropriate error handling
- [ ] I have added or updated documentation as needed

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

@@ -0,0 +1,23 @@
+name: Auto-merge Dependabot
+
+on: pull_request
+
+permissions:
+  contents: write
+  pull-requests: write
+
+jobs:
+  auto-merge:
+    if: github.actor == 'dependabot[bot]'
+    runs-on: ubuntu-latest
+    steps:
+      - uses: dependabot/fetch-metadata@v2
+        id: metadata
+
+      - if: >-
+          steps.metadata.outputs.package-ecosystem == 'github_actions' ||
+          steps.metadata.outputs.package-ecosystem == 'npm_and_yarn'
+        run: gh pr merge --auto --squash "$PR_URL"
+        env:
+          PR_URL: ${{ github.event.pull_request.html_url }}
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}